Tom's Hardware Guide has published the Mother of All CPU Charts. See how your AMD or Intel chip compares to, well, every other AMD or Intel chip:
THG also covers the history of CPUs over the past 11 years.
Part 1: http://www20.tomshardware.com/cpu/20041220/index.html
Part 2: http://www20.tomshardware.com/cpu/20041221/index.html
This is a great reference for finding out how much performance you will gain over your current system, if you upgrade. And it's fun to read the history and see how far we've come in so little time.