Well, this is nice: a Radeon HD 5000 series graphics card available on the cheap. It looks like you're not sacrificing much in performance, either: The $US60 Radeon 5450 has full DX11 graphics and Eyefinity multi-display support.
The $US60 version comes with a 512MB memory configuration, and you lose a little speed compared to the 5800 and 5600 lines. But the 5450 is also optimised for HTPCs, with HDMI 1.3a with Dolby TrueHD and DTS-HD Master Audio.
UPDATED: Hey all! Took down a video that had been posted here previously, whose purpose was to demonstrate what DirectX is capable of. The 5450 does have DX11 support, but I didn't mean to imply that this particular card would give you that exact performance shown in the video. I clearly see how that could have been misinterpreted, though. [BusinessWire]