Depending on what you're doing, you may be able to find a 1U server that will fill your needs. Most of the 2U tend to be the deep rackmounts (24" or so) and pretty heavy... designed for really industrial-strength hosting solutions.

You might check racklogic.com... they have some excellent 1U servers that can hold up to 3 hard drives, take standard motherboards, run cool and reliably. We've got several of their boxes, and the ISP in the cage next to us at the data center where our boxes are has about 400 of their servers. Prices run $500-$1500 depending on drives, ram, processor, configuration, but are generally very competitive.