Current top end cpu's + mobo's would, I guess, be...
Intel Pentium 4 3.06GHz (+ hyperthreading) at around £500 (less if you buy OEM, more if you buy retail...and something like the Asus P4T-533C mobo at around £120.
Or for AMD...
Athlon 'Barton' XP3000 +333FSB (retail at around £480)...
...but this is all silly money m8 !!
Why spend nearly £500 for a pent 3GHz when a 2GHz only costs around £150 ?
Why buy a Barton AMD (that's only just released) at over £400 when a tried and tested XP2100 costs under a ton?
If you want best bang for your bucks, i'd suggest one of the following combos:
Intel Pentium 4 'Northwood' 2.66BGHz (Retail box at £200) and something like the 845E mobo at £100.
Or:
AthlonXP 2700+ (in the £200 area) and say the A7N8X mobo at another £120. (This is the one I'd probably go for if i was buying now)
Shop around on the web of course for lowest prices...I don't know what they are if you're in the US tho! By the time you've read this, prices will all have tumbled again probably. :spin:
I'm sure someone will give you completely different advice and that'll really confuse you.