If your getting a quality PSU, 550w is enough in reality. So the 650 is good for some headroom, but i doubt you'd need it. Your final decision will probably be based on price at time of purchase unless you plan to buy specific parts when they are on sale and not build till you have everything. Greg_77 has a good list of quality units, you can add silverstone to the list also.
Note on your build, if you're planning on an AMD platform, you don't want to get a 6 gig ram kit. Those kits are for triple channel intel platforms. It would work, but you'd have 3 sticks running in single channel and take a bandwith hit. You won't need more than 4 gigs (unless heavy vid/graphics editing) so stick to that. I also wouldn't commit to AMD if you're build goes out to a year. If the i5s are in the same price bracket and have superior performance, you could be missing out. i5s also only use dual channel if memory serves me correctly. Nope, that wasn't intended to be a pun.