Mike Sexton endorsed Party Poker is the proud home of the World Poker Tour, and, unsurprisingly, it has a stellar qualifying program for WPT events. Up until it pulled out of the USA, Partypoker was actually the biggest poker site – a position now held by Poker Stars.
Partypoker is home to very good weekly tournaments. Because their player base is shared across 3 rooms in the party/bwin network, tournament fields and cash games are all filled quickly so there's not much waiting. Their weekly majors are still some of the highest value available.
Partypoker prides themselves on excellent customer service, so you can count on quick payouts and customer support whenever it is needed. They might not have the strongest signup bonuses, but their low rake provides excellent long-term value.