- monitor
- keyboard
- mouse / pointing device
- creature comforts, e.g., chair
- The biggest and best PC monitor that you can afford. You know that you will be spending your life in front of that screen. Pay the extra and get a flat screen. If that means a plasma display, so be it.
- A Dvorak keyboard and wean yourself from qwerty. Or not. In any event you can join the periodic discussions/flamewars on slashdot ( http://slashdot.org/ ) about qwerty versus Dvorak.
- A graphics tablet? Try the Wacom Intuos3 series. The 6x8 and 6x11 are affordable with street prices of approximately $280 and $330 respectively.
- The most comfortable chair you can find. For an affordable chair try Office Max but tryout every chair in the place until you find one that you can fall asleep in. Your neck and back will thank you.
Your backup PC doesn't need to be quite as powerful as your main PC just as long as it is useable for whatever CAD work you are doing (has all of the requisite software installed with licenses and the minimum RAM etc). However, you might want to unclutter your main workstation box by having the DVD/CD burner on the backup box plus several additional large hard drives, perhaps configured as a RAID array. To continue the uncluttering theme, you could use it to run all of your non-CAD apps such as your email client, Quicken, contact programs, calendar, PDA synching et cetera.
Some of us have an even more elaborate CAD strategy: We buy/build a PC for each of our major CAD applications and the box becomes more or less dedicated to that application. For instance, we do both electronic and mechanical design. In that situation, one might have both a SolidWorks (mechanical design) box and a Altium (electronic design) PC.