SilverStone Strider Gold 550W SST-ST55F-G ($120 @ Newegg, $8 shipping)http://www.newegg.com/Product/Product.aspx?Item=N82E16817256085
There is also a 650W version, but that is $20 more expensive and you don't need the extra wattage.
Other PSUs which are modular and less than 160mm deep:
SilverStone Strider Plus 500W SST-ST50F-P
SilverStone Strider Plus 600W SST-ST60F-PS
This is quite new so might not be available yet.
Note that there are two versions of the Strider Plus 600W, the one I'm suggesting is 140mm, but the older, more commonly available one, SST-ST60F-P, is 160mm deep.
Cooler Master Silent Pro M500-M700 are 150mm deep and modular.