2010-11-18 (updated 2022-01-03)
It is presumed that many of these searches will fail to find invalid data.
games with invalid data.
games with UVL maintenance tags
games without a media listed (Disk, Cassette, Cartridge, Download, CD...)
games published by "?" (no publisher) - Note, will not show games with invalid publisher data (such as blank or space)
games developed by "?"
Games with invalid publisher
Games with invalid developer
games without images
games with any image
games with every image type
games with only unknown image types
games without year
games with year only (no month or day)
games without day (has year and month)
games with 19?? style invalid year
games with plain TBA invalid year
games with TBA XXXX style invalid year
As above with 1970s games
As above with 1980s games
As above with 1990s games
As above with 2000s games (but not 2010s or greater)
As above with 2010s games
As above with 20?? style invalid year (but not 2010s or greater)
games without display type
games without perspective
games without gametype
games without tags
games without multiplayer info
games that are not 100%
games without authors?
games without description?
games without reviews?
games without external reviews?
games without UVL content rating?
games without release data?
games without relations?
games without media?
games with media
Games without any cross-references (cross references are currently counted on the platforms pages, but not searchable)
Games with any cross-references
Games without UPC cross-references
Games without SKU cross-references
Steam games without Steam cross-references. For temporary use: This may show a few of them from time to time.
Games with Steam cross-references but not tagged steampowered
Games without [#id] cross-references
Games with [#id] cross-references
games without main images
games with unknown images
games without title images
games without in-game images
games without package images
games with title images
games with in-game images
games with package images
games without character images
games without sprite-rip images
games without game art images
games without animation frame images
games without hardware images
games without detail images
games with undescribed images
games with not safe images
games with only not safe images
games without editor's notes?
games with editor's notes? (Sometimes Main Description information is in the Editors Notes because there is not enough information for a Main Description. The rest of the editor's notes generally indicate a problem with the entry that should be fixed)
games with comments? (should be phased out)
games without cross-references?
games without alternate titles?
games without any user tags
games without my personal user tags (<- that shows mine) http://www.uvlist.net/search?ftag=-%21%25215&ipp=c (replace 215 with your user id)
games played
games not played
games playing
games not playing
games owned
games not owned
favorites
not favorites
games completed
games not yet completed
games wanted
games not wanted
User tags, other user tags, and standard tags can be combined. For examples:
games owned and not yet completed
favorite games with public transit

games without any user score?
games without my personal user score?
entries edited by me (<- that shows mine) http://www.uvlist.net/search?/search?ipp=c&feditor=215 (replace 215 with your user id)
entries created by me
entries not edited by me (games I've never contributed to)
http://www.uvlist.net/search?ipp=c&ftag=!voted_215 Games I voted
http://www.uvlist.net/search?ipp=c&ftag=!played_215%20!voted_215 Games I have played and voted
http://www.uvlist.net/search?ipp=c&ftag=-!played_215%20!voted_215 Games I have not played and voted (oops!)
http://www.uvlist.net/search?ipp=c&ftag=-!played_215%20-!voted_215 Games I have not played and not voted
Games that were created for both, for example, Nintendo NES and Texas Instruments TI-99/4a. ([url=https://www.google.com/search?q="running+on"+"Related+games"+"%28NES%29"+"%28TI99%29"+site%3Auvlist.net]sloppy solution that relies on a game relations entry protocol that not all UVL editors use[/url]
games without any Activities tags
games without any Cartoon/Anime tags
games without any Culture tags
games without any Creatures tags
games without any Fiction Genre tags
games without any Game genre tags
games without any Hardware tags
games without any Historical tags
games without any Locations tags
games without any Music tags
games without any Software tags
games without any Sport tags
games without any Tools tags
games without any Traditional Games tags
games without any Vehicles tags
games without any Video game tags
games without any Other tags
games without any direct descendants of a specified parent tag?
games without any descendants of a specified parent tag?
List of gametypes not used for any games of a platform.
List of tags not used for any games of a platform.
games without titles matching their languages?
games without language?
Japanese language games without Japanese script title?
Chinese language games without Chinese script title?
Korean language games without Korean script title?
Vietnamese language games without Vietnamese script title?
Arabic language games without Arabic script title?
Greek language games without Greek script title?
Persian language games without Persian script title?
Hebrew language games without Hebrew script title?
Russian language games without Russian script title?
Ukrainian language games without Ukrainian script title?
Bulgarian language games without Bulgarian script title?
Serbian language games without Serbian script title?
Croatian language games without Croatian script title?
Siamese language games without Siamese script title?
Games in only one in language
Games in multiple languages
Games in [language] This is now a filter on the search page
Games not in [language]
Games only in [language]
Games published in [Country]
Games not published in [Country]
Games only published in [Country]

characters that don't have a group or are linked to non-existing group
articles that don't have an entry or are linked to non-existing entry
articles without titles
relation entries that don't have a game or are linked to non-existing games
games with tags without groups
tags without groups

Very specific searches:
Tandy 1000

2013-01-01 (updated 2013-01-01)
This is a good idea, I'll update your post if any of those is possible, and congrats for figuring the no tags, I didn't by myself!

-edit-
This wasn't in your list, so I put it here:
games with media

2013-01-03 (updated 2013-01-03)
Note that games without developers are not entirely covered (the developer field is empty sometimes and does not include a question mark).
Same for publisher, although it is more rare, for example : King Kong, Rock Star Ate My Hamster.

You could add :
games with UVL maintenance tags
games with image that do not have an in-game image as a main one (maybe something shorter!)

(NB : url markup is broken when square brackets are included in the link. I wanted to add "&fcols[]=g" at the end of the url).

games with not safe images

Did you mean "games with not safe images only" ?

2013-01-03
re: Usefuly links
It is presumed that many of these searches will fail to find invalid data.
games with UVL maintenance tags
games published by "?" (no publisher) - Note, will not show games with invalid publisher data (such as blank or space)
games without developer
games without images
games without year
games without perspective
games without type
games without tags
games without multiplayer info
games without authors?
games without description?
games without language?
games without reviews?
games without content rating?
games without release data?
games without relations?
games without any user score?
games without my personal user score?
games without any user tags?
games without my personal user tags?
games without media?
games with media
games without main images
games with unknown images
games without title images
games without in-game images
games without package images
games without character images
games without sprite-rip images
games without game art images
games without animation frame images
games without hardware images
games without detail images
games with undescribed images
games with not safe images
games with only not safe images
games with "comments".
games without editor's notes?
games without cross-references?
games without alternate titles?
games without titles matching their languages?


WOOHOO! I figured out no tags. Duh! It was so obvious. But now I can fix my entries that I goofed the tags with. Seems that I sometimes paste tags into the author's area.

2013-01-04
games without content rating?

tag: -rating-%
The "old" ESRB rating that was automatically filled was never searchable, and I suspect it's going to be phased out or modified.

games without any user tags?

tag: -!%
All user tags start with exclamation mark.

games without my personal user tags?

tag: -!%_#
Just replace # with your user ID which is found when you look at the game listings with one of them.
Like for me that's -!%_10036

2013-01-12
Is there any way users can have access to this:
http://www.w3schools.com/sql/sql_null_values.asp
from the text search fields?

2013-01-13
Due to quoting and escaping queries, I don't think so, unless Andrea adds an option for it.

2013-02-14
The underscore is important in the personal tags queries to prevent user 6 from getting results that include user 76, 146, and such.

2013-04-19
I think a games without [#id] cross-references would be quite useful

2013-05-14
Listing tags without their page set up ("red tags") is missing as well. These are either bad tags (typos, nonsense or missing alias) or tags that are/were waiting for more games before setting up the page. You can currently find them by browsing the tag resource pages, but it's very time consuming to go through them.

2013-05-15
Edited the OP's title because "usefuly" is not a word, and this thread keeps getting back up.

2013-05-17
Videogames isn't a word either. Trekkie, Ginormous, smackdown, spyware, emoticon, unibrow, crunk, ixnay, and biodiesel weren't words at one time either. I chose "usefuly" on purpose. Its a entirely cromulent word.

2013-06-24
What is the company ID for a game with no publisher or developer? What if "?" is entered? What if invalid data is entered? And can we search for these values?

2013-06-26
0 is usually reserved in SQL databases, so it would work fine for that as an alias if added as such. Otherwise I don't think there is one.

2013-07-29
Should 19??, 198?, 20??, 200? type year entries be banned from being entered from the game entry and edit page?

I think they should. Attempting to do so would disable the [Game Update] button and also suggest adding an Editor's Note about the approximate year.

2013-07-30
Just block or filter out plain numbers, that should be good enough.

Would require renaming 007 tag and similar, but that should be renamed anyway.