Yahoo and Pogo are good sites to play against real people for fun. Why would you want to play for real money? Could you imagine the 'botting occurring and 3rd party software?
You'd have to be a moran to play strangers online for real money. Comps are fast enough now (and can be configured easily) to play blitz 3/0 at 2000+ level.
that being said, chesscube is a great easy to use site that does an OK job tampering cheating ... fics is good too, high traffic, but fairly limited to sub 1700 players.
. Just kidding.