^5 +1 what gkay and invisik said.
I have the XFX Radeon HD 4770. It's a good mid-level general purpose card and it does not use very much power. It's only 8.5 inches long and requires only one 6 pin PCIe power connection. Technical reviews have been very favorable and Tom's hardware did an article about using two of the cards in Crossfire mode. You just have to remember it is not a high end gaming card.