I play mainly at Ultimate Bet, but also at Pokerstars and would recommend both as excellent sites for the reasons others have already mentioned- good software, reliable service.
UB has more low-limit tables at the times I play, which is why I play there more often, although I slightly prefer their interface and the Ultimate Buddy program is very handy to keep track of the fish .
In terms of deposit bonuses, UB has a refer a friend deal on at the moment (50% up to $50 for you and double this for the person who refers you)and PS has a 20% deposit bonus at the moment.
