I've had good experiences with Gigabyte. But Asus is supposedly the best of the best.
About the DDR2-800 situation. You won't be able to even get the memory to run at DDR2-800 unless you overclock the FSB of the board to 800Mhz. That's processor can handle it, but you'll need to give it a LOT of extra voltage and water cooling. Once you get the Conroe, it "should" work fine at DDR2-800. You won't run into any problems at DDR2-667 speeds though.