Just to clear up my bookmarks!
Social networks to meet people abroad (Couchsurfing, InterNations, TravBuddy, WAYN, Be Welcome, GapYear, TravellersPoint, Link Expats):
NomadWiki (this is basically heaven, if I ever took the time to read it):
Educational exchanges… Probably for underage only, but check it out:
Teach for All: