I'm doing my first build and am looking at PSUs. So far, I have
AMD Phenom II X2 555 BE
MSI 785GM-P45 AM3 mATX
EVGA GT240 DDR5 512 GB
Samsung Spinpoint F3 1TB 7200 RPM SATA 3Gb/s
Lite-On SATA iHAS124-04 CD/DVD Burner
Antec 900 Case
I will be picking up 2x2GB memory in the next few days. Also, I may try unlocking the X2 but will probably not overclock. The computer is mainly for office and some gaming (Mass Effect 2, Starcraft 2 - I'm aiming for a budget build so low to medium settings are okay). I will probably not be upgrading in the near future (at least not for 2-3 years) except possibly adding on another hard drive.
Right now, I am trying to decide between Corsair 400CX and 650TX (going for $30 and $65 at Amazon). Any recommendations (on PSU or on build in general) would be appreciated.
Your graphic card is not the best for gaming...
Anyway, if you are not thinking about upgrading your GT240 for a high performance gpu, the Corsair CX400 is a good choice (it is able to handle even an ATI 5770 if needed).
As said already, a Corsair 400W would suffice for your build.. However, its always good to have headroom when it comes to a PSU selection.. Helps in moving upto bigger and better things in the future.. Keeping that in mind, i'd suggest you to get the Corsair VX 550W if it fits your price bracket..
P.S. - Do not count on the core unlocking feature.. They sometimes work and sometimes don't.. Go for a true quad instead.. Check out the Athlon II X4 635.. Its pretty decently priced..