This one (answers.com) is one; then, there are lots of wikis and discussion groups. For example, you can contribute to Wikipedia. You can also search for discussion groups in any area that interests you.
gracieandranda.webs.com
bungie.net?
tracpeople.moonfruit.com tycanyon.moonfruit.com
KandeCorn.Piczo.Com
Coolmath.net
There are many "Cool" virtual game sites.
didgi draw on crayola.com
http://www.teenchat.com/
Daily booth
Dragon world . Com
cool math.com farm five.com addicting games.com whack your ex.com
some good websites are addictinggames.com primarygames.com miniclip.com cartoonnetwork.com