I use to go through keyboards like candy. I've owned just about every kind. Ergonomic ones hurt my fingers, but helped my wrist. Plain flat ones worked ok, but hurt my fingers got tired after a while because of the weight of the keys. I preferred a back lit one because I work in a darker environment.... and I occasionally have to look at my keyboard for special characters. I'm big fan of standard layout keyboards, built in USB ports, and built in media keys/volume control. I'm a big fan of this article and this article. They helped me come to some great realizations about keyboards.
A little over a year ago, I "took the plunge" and spent close to a hundred bucks on a mechanical keyboard. It's been worth every penny. The key presses are extremely light with a tactile response. I've been able to pull 12+ hour days typing with minimal hand fatigue. It has also shown minimal wear over all the heavy use.
If you really think about it, your keyboard is the most critical piece of your PC setup. You shouldn't hesitate to invest good money into one. If you are a hiker, you can get by with cheap equipment, but you have to have good boots or you will have a miserable day. A high quality pair of boots will keep you comfortable and last you a long time. A $150 mechanical keyboard should last you multiple computers. I'd highly encourage anyone who works all day on a computer all day to invest in one.