I've got an account on pacific poker, seems alright. My favourite is royal vegas at the moment, haven't put any money in and I've got my free $10 up to nearly $100 now (taken $50 of that out).
Pokeroom has probably got the best software, I'll probably try pokerstars some time.
Pokerstars is a bit of a bad one for withdrawing cash.
You have to wait 48hrs to take anything back out and it has to go via cheque or you have to sign up for one of two online payment scheme things like Paypal.
That said despite the horrible software it's an easy money maker.