There are a lot of websites that maintain lists of improv games. Some are large, comprehensive lists, others aren’t much more than a list of names that a troupe performs. Some are being updated regularly, others haven’t been touched in years.
These are sites I find useful. There isn’t a single site that I go to for all games. Some lists are more comprehensive than others, but I still like going to the smaller sites for unique takes on traditional games.
Keep in mind that the names used for games vary from region to region, and sometimes from group to group. Also, variations on games are common, so the description you find on one site may not match a description on another site, or the way that I teach the game in the workshop.
Improv Encyclopedia has the most comprehensive list that I’ve found, and provides the games either alphabetically or by categories. They also try and list the games under all known names and variants. I use this site most often.
IRC Improv Wiki includes some sketch and stand up comedy references, but it has a lot of games and exercises.
Improwiki is new to me, but I really like the layout. They have a pretty good list and many of them include short video clips of the game being performed.
Learn Improv also has a great list of games broken up into Warm-Ups, Exercises, and Handles. It’s got good descriptions and a nice format.
The Living Playbook is a very old site (dated 2001) that’s just a big, text list of games. The descriptions are short and not very comprehensive, but I’ll scan the site from time to time to see if there are any nuggets worth mining.
Long Form Stuff Shaun Has … this is another old list that at least has an index at the beginning of the big text dump. It’s a list of long form structures that Chicago’s Shaun Himmerick has collected from a variety of sources. The descriptions are pretty good although brief.
Fuzzy’s Games List is yet another old list (why did so many stop in 2001?) that’s worth browsing from time to time.
Bring Your Own Improv contains a list of the games this performing troupe uses, and it includes some delightful variations.