That 3770k might max out at 150w at a nice overclock. The 7870 might run a good 240 or so while the other stuff in a basic single HDD and 2dimm set of ram with a CDRom drive might run 60-100w. I wouldn't imagine you need more than 500 but it's always best to go with something good. Avenseth has made some nice recommendations but I just want to throw my vote out for the Corsair. That's a very nice PSU. I have always had the best luck with Corsair and Antec power supplies so getting yourself a 650w for that price with a decent Bronze rating is a good deal. Also you'll have plenty of overhead for a better card later on after the 7870 ends its life.