For the next 48 hours (basically, today and tomorrow) you can download Texas Hold'em free from the XBox Live Arcade section. After that, Microsoft will be charging 800 points for it.
It's a good deal. Especially since you can't wager real money, so you get the fun of playing cards without the financial ruin. ;)
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.