I don't know where you're from but I'd go with
PartyPoker if you live outside the US. The standard of play in cash games upto $0.5/$1 level is very poor, and completely teeming with fish, plus there's always action to be found all day long.
If you're in the US, I'd recommend
PokerStars, as this site's also teeming with fish, but I personally like Party better.