If you need a bit more than the 450W you can get from the Corsair VX450W, try the Zalman 600W HS Heatpipe cooled PSU.   From the testing at Hi-Tech reviews, by choosing the Zalman you get a fairly reliable PSU, whose 120mm fan does indeed keep the noise down while still providing an exit for the hot air in your case.

If that isn’t the PSU for you, but you still aren’t looking for a kilowatt, then maybe the Enermax Liberty DXX 500W that Lee just finished reviewing might be more to your taste.
“Not everyone is building computers to sit on their desktop or next to their table, some of us are actually building computer to record and watch Television with it. When we do, we need a power supply that is far quieter than the normal ones and that is where the Zalman ZM 600 HP 600 watt Heatpipe Cooled Power Supply comes into play.”

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