The best CPU for power gaming is nVidia GeForce3 or the upcoming Radeon2.
The general processor is far less important as both Intel & AMD both have extremely fast processors, which provide plenty of juice.
If you are a real serious gamer focus your dollar on your video card, sound card, monitor, speakers, joystick, mouse, keyboard, desk, chair & internet connection.
The best thing to do is buy a motherboard with a long upgrade potential and get a reasonably priced CPU. Then just slap in new processors as the price comes down and your gaming justifies the increased power.
If you are favouring P4 then ABSOLUTELY wait for Northwood, it's not far away and it will provide a good upgrade path. AMD T-Bird is a great buy today, but possibly not as inspiring once Northwood appears, then again T-Bred should be a direct upgrade from T-bird so either way you have a long future of awesome gaming. Good Luck.
<font color=blue> The Revolution starts here... as soon as I finish my coffee </font color=blue>