Short answer:
How much horsepower are you looking at?
Under catagory of "best bang for the buck" is the Barton core Athlon 2500+.
As for Intel stuff, the 2.0Ghz celeron and 1.4Ghz P4 benchmark almost identically.
Long answer:
http://www6.tomshardware.com/cpu/200...mparison_table
Toms is always a good place to go for hardware questions.