I'll second mining in a pool. For a beginner deepbit is nice and stable.
For graphics cards that are readily available, I'd look at the 6870. You're looking at at least 2.2/mh per watt when properly set up and you can get them for about $160. For less money the 5770 is very nice too.
The 5830 is cheap upfront, but it's inefficient.
It's not inefficient by much. There are a lot more inefficient cards past the 4xxx series.