Computer desk or paperwork desk? Experiment to get the right height - it's important. How tall are you? How do you sit?
If computer, remember that the monitor should be at eye level. Monoprice.com has the monitor mounts cheap. Proper keyboard height and angle is what keeps carpel tunnel away.
My desk is built from 2 x 8s on cinder blocks painted glossy black. It's not sexy but it was cheap and is solid as a rock.
ETA:
How about these :-)