And there is no way you can go with just a fan on a cpu, it would most likely overheat instantly. I would say a heatsink with a fan over just a heatsink, unless you have really good airflowin your case, so that you get the heat away from the heatsink so that the heat dissipates, helping cool the cpu.
And if you have not bought the cpu yet, if you can wait until the conroe release x2's are supposed to drop in price by 50%.