If you really think bitcoin will pay out for you, trying a 7950 or a 7970 might not be too bad (these cards just came out so they do charge a small premium....). Besides that, I will have to agree with the 5830 (or a 5850 /5870 if oyou can find one)

About companies, I heard horrifying things about XFX's AMD customer service, so I have been told to stay away from their ATI stuff, but I'll leave that decision up to you.