If you only plan on running a single HD6770 then a quality 400 watt power supply would be fine. You could actually get away with a 350w power supply. If you ever plan on upgrading the graphics card you can run just about any single graphics card setup with 550 watts.
Stick with Corsair, Seasonic, PC Power and Cooling, XFX, Enermax, Silverstone, OCZ and Antec for quaity.