Sparkle Power Supplies do not have on/off switches. I used one for a while. They are used in hospitals and medical centers around the world for their reliability and quietness. Not too expensive, but more expensive that those shitty RAIDMAX or POWMAX jokes.
http://www.sparklepower.com/proPCPS_ATX.html
Check your local vendor for these PSUs, or just order one from a reseller.