I've used eLance and odesk before - but the issue with elance is a lot of people are catching on that they should be charging more for their VA services. You can find some, but the really reliable ones want $5/hour (lmao why am I complaining about $5/hour?)...
The other stuff posted here is good, too, I'd just check all the places you can think of until you find the best deal with some provider feedback on people so you don't get one of those VA's that says they took 40 hours to manually create 30 web 2.0 accounts and post content to them, or just stops communicating with you all together because of a fake language barrier, or real one, either way.