PokerStars and Full Tilt Poker both just got busted by the FBI. Thousands of players are looking for a new home as neither Stars nor Tilt can be expected to get back online, ever. Luckily you can still find a couple of sites offering poker to US players. True Poker and Doyles Room are the best known brands.
Doyles and True both offer poker to US players and they have been doing it for a long while. True is one of the absolutely first rooms online, way before Pokerstars and Full Tilt Poker so You can count on them staying online for quite a while.