I personally use an ABS Tagan BZ 1100W power supply with my UD3P and Q6600. It's about $300 but the quality and value is incredible and it's future proof for at least a few years. It might be overkill for you but I run a crossfire setup of two HD 4850 X2's. This PS is probably one of the best products I've purchased.
Depends on what else you are powering, but in a good starting point is an Antec or Corsair around 500W. I am a loyal Antec user, but Im about to upgrade to a Corsair with higher rating due to new system and lots of drives.
I have a 430W PSU powering a B3 Q6600, ATi 4670, 2x 1TB HDD, P43 Gigabyte board with 4x 1GB sticks of ram and a plethora of PCIe and USB TV cards. It acts as my HTPC and the PSU fan does not break a sweat even when using the CPU for encoding. Oh, this is water cooled as well with a pump running from the PSU and 4x 120mm fans on ultra slow speed to keep the noise down.