http://bit.ly/S9ZetNCheck the first link.
For the record, that first link was for ones that are only 11" deep, there are other Billys for $20 that are 15 3/8" ... much better value and hold a lot more weight!
Surprised no one mentioned the sauder 5 shelf staples unit I've had them for five yrs no sagging. Prob is that the middle shelf can't be moved, other than that it's a great product usually it's $149 but goes on sale for 119-100 all the time.