The motherboard to get now, is the Gigabyte P35-DS3R
, if you're not planning on SLI.
If it's between the Q6600 and E6850, I would pick the Q6600, because sooner or later, games will be supporting more cores. At the price of around $270, for a quad core. That's hard to pass up. With good aftermarket cooling, and good airflow, you can get that Q6600 past 3.0GHz.