E21XX paired with a P35 chipset. My pick was Gigabyte DS3L and an E2180. Abit P35-E is popular, so is the MSI Neo2. If you're willing to overclock (and you should be) you'll get a bit more performance out of this bad boy than a x2 6400+. With some luck you should hit anywhere between 3 and 3.3 ghz with the core2 with the stock cooler and cheap ram. Plenty of CPUs here to choose from including quad cores, if you want performance Intel is where it's at. Come on over to the CPUs and overclocking forum for a read. There's a thread including OCs anandtech forum members got with these chips ranging from mild (2.6 ghz) to wild (3.6 ghz).
If by hottest you mean temperature rather than overclockability/reliability, we got plenty of nvidia chipsets here on the dark side.
To sum it up:
680i, 780i, 790i, 750i + intel: the only way to get SLI on intel, but may be problematic or poor overclockers. Hit and miss support for 45nm CPUs.
P35 + intel: Limited to Crossfire (AMD) for multi-slot GPUs but work great with nvidia single slot cards. Support 45nm duals and quads.
770, 780G for x2, phenom: budget, most not for use with 125 watt cpus. Comparatively great on-board video with the 780G.
790X and 790FX chipsets for x2, phenom: your choice for Phenom and other 125 watt CPUs like the 6400x2. You can stuff a lot of video cards into the right 790FX board.
nvidia chipsets for AMD: not familiar enough to opine