This is an interesting article from Lifehacker. I designed my own desk, and had a carpenter friend throw it together for me recently. I was actually downsizing, my previous desk was a colossal corporate office style desk that was simply so big as to be impractical for the space available. I wanted something simpler, something smaller and something a little more designed to suit my own comfort. In particular I wanted the desk to be much taller than most.
Ergonomics is often the last thing we think about when we buy a desk, but it should be the first thing and the last thing. We tend to prioritise what will fit, what is affordable and often what has the most built in storage. Those things are important, but should all be judged with regard to your comfort. If you're anything like me at all, you are going to place your posterior in a chair pulled up to your desk for a significant portion of your life. You deserve to spend that time as comfortably as possible. Make sure your chair and your desk work for you.