PSU calculators and brands! Help!

Any quality 450w PSU would run that setup fine.
As for whats a good PSU, check out reviews at sites like JonnyGuru, hardocp, hardwaresecrets... Most brands have good and bad PSU's.

500W.

A decent one, not some Logisys or Diablotek one.

Best brands are Corsair(CX500), other brands would be more expensive for no benefit(for this build), like Seasonic.

500W.

A decent one, not some Logisys or Diablotek one.

Best brands are Corsair(CX500), Seasonic, LEPA, Enermax, or PC&P.

Hi - aerocool - not cool, most of their units are made by HEC & Andyson,
both have a less than stellar reputations.

pop is right - find a decent brand & model (450w or a little more),
and check in here if you don't find a quality review.

Quality brands: Seasonic, XFX, Antec, most Corsair's, most Enermax,
Rosewill Capstone series, Silverstone, PC Power & Cooling, and some others.

Calculators are probably dead accurate, assuming you can give them accurate input.
Unfortunately, some inputs are unknowable.
Capacitor ageing factor for instance?
Or, how much reserve do you want?

It turns out that for a normal pc, it is the graphics card that is the determining factor.
Here is a handy table of graphics card/s and their recommended psu requirements.
It assumes a normal complement of cpu and peripherals.
http://www.realhardtechx.com/index_archivos/Page362.htm

It is not wrong to overprovision a psu by 10-20%
It will tend to operate more efficiently and quieter in the middle third of it's range.

Whatever, buy only a quality psu. Cheap psu's may not deliver advertised power among other deficiencies.
Here is another handy chart for psu quality:
http://www.eggxpert.com/forums/thread/323050.aspx