Flying cross-country twice over the past week gave me a chance to spend a little more time with the Texas Hold'Em app for the iPhone. While a great application, unfortunately the AI is very weak and easily beatable, even in the tournaments with the most expensive buyins.
iPhone and iPad apps tagged "card game."
Texas Hold'Em iPhone App
Currently holding the #1 slot in the iPhone app rankings is Texas Hold'Em.
Apple's poker simulator is a great time-waster, whether you're playing the single-player mode or playing against your friends.