One of the best purchases that I have ever made is the Kinesis Advantage keyboard.[1] In fairness, I was tempted to return it shortly after purchasing, but opted to give it one full week of use before making my decision. It took a couple days to become comfortable using it, and now I can't think of myself using another keyboard. It's designed for optimal physical placement of ctrl, alt, delete, backspace, and spacebar, among other keys.
[1] http://www.amazon.com/dp/B000LVJ9W8