PowerPC : An Architectural History [arstechnica.com]

This is brilliant! Part 1 of 3, this article looks at the first PPC ship, the 601, and how it was designed to bridge from POWER to PowerPC, then continues to cover the rest of the 60x line.

If you're into processor design you will love this series. The same author has apparently written a more in depth history of the Pentium line, but I like my processors in RISC thanks ;)