You have quite a generous allocation for your components - I calculate the dollar equivalents to be $320 for cpu, $320 for motherboard, $150 for RAM, and $150 for video.
I would recommend
i7-930 cpu
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115225 $290
Gigabyte GA-X58A UD3R motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128423 $210
OCZ Gold 6GB DDR3 1600
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227365 $150
Asus EAH5770 Radeon video card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121363 $150
The cpu will provide plenty of processing power for multiple tasks and encoding, 6GB should be enough for your applications like Photoshop which can use more RAM, if you run a 64-bit OS to make use of all of it, and the 5770 video card will handle any graphics need, even most 3D games. You can get by with a less expensive setup if you choose a P55 socket 1156 motherboard and an i7-860 cpu, which will still be close in processing power, but not as upgradeable.