Here's what I did with my setup. It's a little different situation because I have a 200A main breaker box with plenty of room.

Here is the new 60A 220V breaker added to my main box with a 6awg 3 conductor wire leading to my sub panel:
http://i.imgur.com/uxO8y4C.jpg?2

Here is my sub panel. I decided to go with 15A 110V breakers with a single breaker per 1000-1300W power supply. I used 14 awg nema13 power cords and cut them off to wire them directly to the breakers, thus saving money on recepticals, outlets, boxes, condutit, etc. I checked with a couple power guys and everything seems to still meet code.

http://i.imgur.com/qflcK84.jpg?2

Here is the box all covered up. The big 'breaker' with the white label is actually a whole home surge protector. I didn't want to waste my money on PDUs or individual surge protectors so this was a good solution for everything on the sub box.

http://i.imgur.com/292lBzj.jpg?1

Here's the whole cabinet. Obviously this is a little easier to do in a cage but could pretty easily be mounted on a wall next to your shelf-type setup.

http://i.imgur.com/9BY0AcL.jpg?2

http://i.imgur.com/szIaOjW.jpg?2