Adrenaline Pool Online. You can play 8-ball, 9-ball, straight pool or snooker against other folks online. You can't have a custom screen name or play against the computer unless you buy the full app for $4.99, but the Lite version is good enough for now.
It tracks your games and keeps a separate ranking for you in each game. Also tracks the time you've spent playing.
My nephew, brother-in-law and I were playing quite a bit over the vacation week.