I see all of these different companies selling the HD5850 (Gigabyte, XFX, HIS, etc.) - which one do I buy from? Is there even a difference, except for looks?
No, there is no difference between each brand. XFX does, however, offer a XXX and black edition version of the 5850, which are essentially cards that are factory overclocked. Stick to the regular ones for the must bang-for-your-buck. Mirzai_m's catch is quite nice!