2.4GHz at rock solid stability is simplicity with the X2 3800+ on an Asus A8N-SLI Deluxe.
Lock the PCI (33.3MHz) & Memory clocks (DDR400) and simply set the FSB to 240MHz. Mine runs here using the stock AMD cooler included in the package at 2.4 at 40C idle, ramping to 53C under full load of both cores. You may need to drop the HT multiplier to 3X though, but using the same components on each system I have done this on, some run fine at 5X or Auto, yet others needed to be dropped to 3X. Have managed 2.6GHz using the Stock cooler but wasn't 100% stable whilst under full load for long periods of time (anything more than 15 minutes would cause the system to halt - no BSOD, just frozen up).
I am using 2 x 1GB DDR400 Kingston ValueRam Modules that I bought 2 years ago.