Recommended power supply for my computer

Hi guys,

Here is my (soon-to-be) rig:

Mobo = ASUS M5A97
CPU = AMD Phenom X4 955 Black Edition
VGA = Nvidia Geforce GTX 550 Ti
RAM = 2 x 2gb Corsair DDR3 Value 4GB PC10600

all that's left is the PSU, which is i'm confused on

i've already calculated it on the PSU calculator, and it turns out i only need maximum 400 wattage.

should i take 500w or should i go straight to the 600w so that i don't have to buy again later?

which brand should i take?

i got around $75 for budget.

and it have to be the modular one, cause i like when its tidier  

Thanks.