Improv Encyclopedia is the largest collection or resources for improvisation theater on the web. Here you will find tons of stuff related to improvisation theatre.
For those not particularly looking for improv-related material we feature:
This site is organized in 3 large sections:
If you want access to the material when you're off line, you can download the whole site, either as HTML, or as a PDF Booklet. We even have a version for your PDA.
And best of all, it's free!