Raise your desk so you can stand while working. I did this for my home music studio because I stand while playing keyboards and guitars, and found I really liked it for all types of computer work.
Check out my other various ergonomic Instructables:
Ergonomic Work Station, Standing Desk, How to make a vertical, ergonomic (tie-fighter) keyboard, and Create an Ergonomic Standing Desk and Office on the Go.
Step 1: Measure and Test the Height
I wanted the desk high enough so I could comfortably write on it and position my computer keyboard at an ergonomic level, but not too high that I couldn't sit my laptop on top of a monitor and use both.
I tested the setup with milkcrates for a few weeks before refining and committing to a final height.
Step 2: Modify Existing Legs
I drilled holes in the existing legs, and bolted on 2x4s with rubber feet.
Step 3: Reinforce
The extra tall legs were pretty wobbly, so I strengthened them with some steel cross-bracing. The steel is 1/8 x 3/4.
Bend approximately 2 inches at each end of the steel to 135 degrees and drill two holes. Screw the steel to the desk and the legs forming a triangle with each leg. Triangles are much stronger than rectangles because to change the shape of a triangle you need to change the length of its members; a rectangle can change shape just by changing the angles between its members (making a parallelogram).
With the cross-bracing my desk feels rock solid.