Currently, I'm still using a AMD Athlon 64 5000+BE (@ 3Ghz) in an AM2+ motherboard. I'm upgrading that soon with a Phenom X3 740.
I also have a G4 Powermac running OSX (awaiting MorphOS 2.6) and a n eMac running MOS 2.5.
What would I like as my main rig? I wish I could say it was an more power ful PPC machine, but that still a hobby. If I had $300, I'd probably by an X6 Phenom.