Chieftec make/sell a short atx PSU for use in there small mATX cases, it's not on there site but I know they make them
I've found the 270w version but I know they do a 350w one as well, not sure if it goes any higher
http://www.sagemaster-shop.co.uk/aca...I_A300P_3.html
Seasonic used to make PSUs that size as well