I wouldn't go SLI/Crossfire. Not only you add an entire level of troubleshooting in the mix, but also the gain from it usually isn't worth the cost, except if you running games at 1920X1080 and higher. One good graphic card will do fine, and you won't need expensive motherboard and power supply.
I'm very pleased with my Q6600. AM won't take advantage of the multicore when working in the program, but you can launch multiple instance and render multiple frames (up to three, you won't see any performance hit). Intel just released a new line of CPU, the Q9XXX, which would be a better choice if you'd buy it today.
A faster dual core E8400 wolfdale would also be a very good choice, depending on how you use AM and if you have any program that can take advantage of a Quad.
For the motherboard, I can recommand the GA-P35-DS3L from Gigabyte as a solid inexpensive choice.