Hugh McLeod`s list of Improvizational Theatre Structures used to be at www.staircase.org/structures and it contains over 100 Improv games, each with nice descriptions, and classified in 4/5 categories.
The site has been revamped, and now has its own domain name: go to www.learnimprov.com
Being on the tightrope is living; everything else is waiting --- Karl Wallenda