I like to play around on wikis during my brief moments of free time at work. Besides the big one, there are a few others that I have found that are either of interest, or show potential.
Thelemapedia - About thelema, Crowley, etc. A fair amount of entries, but not very active.
dKosopedia for those interested in US politics.
Archaepedia - an archaeology wiki. Not much there, but has potential.
Fans of Strongbad and the other work of the Brothers Chaps will find all they want on the Homestarruner wiki.
Biocrawler has an excellent biology wiki.
Wikitravel is a good resource (by and large) for travellers.
There's not much on this Science Fiction wiki, but it has potential. Ditto this wiki for the Buffyverse.
The International Nath Order has a fine wiki regarding their lineage and tantric matters.
Any ones you recommend?