LairBob - Standing Desk
This is the more efficient approach I've adopted recently -- I basically keep the monitor at a fixed height that works great for both sitting and standing, and then just put a plastic bin and wooden shelf under the keyboard / mouse to raise them when I want to stand. Very crude, but very effective.
Ergonomically, the only two other things I've done are to make sure I'm taking care of my back -- using a pair of shoes with good arch support, and having a cheap bar stool that I got on Craigslist, that I can lean back against as a way of changing up my posture when I'm standing. Like I said...crude, but really effective (and basically free).