Evga, the brand I linked to for the 8800gt, is arguably the best. Lots of people here will attest to that too, they always do.

Usually one of the cheapest as well, but it is in no way the only option.
lol, power supply unit. You know, the thing you plug the power cord into?

Open up the case and take a gander at the sticker on the side. It will list wattage and a little chart that shoes several voltages (+3.3, +5, +12, -3.3, -5, -12v, positive and negative voltages etc) and their respective currents or amperage. The +12 amperage is what you should look for. It'll be a number with a little a next to it.. Also, just to note, there could be dual +12 rails, post both if there is, though this is doubtful.