In my HTPC I'm using a Radeon 5450; but since the 5450 is based on the Evergreen chipset I've been using the propriety drivers (x11-drivers/ati-drivers). Not a fan.
However since the Linux Kernel 2.6.34 release, it appears that progress is really coming along on the open source drivers (see point 1.11 in the link). I look forward to ditching flgrx soon. :)