Party Poker Online

This is a screenshot of a limit Hold'em game at Party Poker.

Party Poker Profile

Games Offered:
Texas Hold'em, Omaha Hi, Omaha Hi/Lo, Seven-Card Stud, Razz

Pros:
Party Poker is the biggest, most trafficked site out there, with over 40,000 people online at peak hours. Which means there's always, always, someone playing what you want to play. Their software lets you add players to your "buddy list" so you can mark easy players and friends and then find them using the player search feature. You can play at more than one game at a time, and take notes on players too.

Has 24 hour online support.

Cons:
Windows-only.