And do you have a preference for AMD or Intel?
For AMD, a Motherboard based on the VIA KT333 or KT400 chipset, or the NVidia nForce2 chipset - with PC2700 (DDR333) memory, and a 333FSB CPU (could use DDR400 RAM, but price/perfomance probably not justified). Dropping back to a less extreme 266FSB CPU (eg. an XP2200) shaves a lot off the price.
A good principle is always to get parts that are NEAR the top of the range, but without paying the ridiculous prices at the very top - and no good blowing most of your budget on a single component.