Are you planning on getting a discrete video card/GPU? Or planning on just using the integrated graphics. Otherwise, something like a 430W efficient PSU (there's a variety of brands like Seasonic, Antec, etc.) will be more than enough for a basic build.
If you're going to be doing any further upgrades on it (E.g dedicated graphics card) then you should be getting at least a xfx 550w core edition PSU (its one of the PSU's that seasonic makes) If not, Like drg889 said.. You're okay with a 430w 80+ rated PSU
i5 - 3570K
Corsair vengance 2x4GB 1600MHz RAM
120 GB ssd (PNY XLR8)
It will have three case fans (HAF 912 case (2x200mm, 1x120mm))
System will be running windows 7 if that helps
I have heeded warnings not to skimp on the PSU, so what sort of wattage will I need and from experience what is the best make/most reliable?
Hi - 350w will power what you have - Even tho you are not adding a gpu at this time
you will most likely do so in the future. A quality 500w unit will allow
you to run a system with any current gpu out there below amd7970 or NVidia680,
and even those if it has sufficient +12v amps
emphasis on quality - if you buy too cheap, you will usually have to buy
twice or more.