This is a good place to start.
This is a tough build. You need a strong CPU and storage system for doing the editing, but you need a strong GPU for the gaming. If it was one or the other (or you could tack $200 to the budget) then you could build a much better machine, but as it is it will not be bad, and you can always tack on upgrades in the future. OC and SLi are not options at this point, but I will try to keep it open to have those options down the line if you want them.
ASUS P8H61-M, no OC, no SLi or xFire and a max of 8GB of ram (technically 16GB but 8GB modules cost too much), but other than those upgrade limitations this board is perfect for you. When things get slow you will want to upgrade the cpu and gpu. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Power Supply: $80, $55 after rebate
OCZ 550W, 80+Bronze. I get a lot of flack for suggesting these, but the new ones are quite good, and the rebate is great, just go in with the understanding that they have been a crappy power supply company in the past, but have been 'remaking' themselves the last few years. Should be more than enough power for any single GPU you throw at it. There is a modular version for a few $$ more. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
I do not like to suggest cases, as your case is personal to your own taste and budget. I use the Thermaltake V3 Black which is $35 after rebate right now and it is housing 3HDDs (soon to be 4! Almost ready for that SSD finally!), an i7 with a Hyper212Evo cooler, a 750W power supply, and a GTX570. I have 7 fans installed (including case and device fans), and it is quiet and cool. Loudest things are the 3x7200rpm drives (seagates are not exactly silent operators) and my 570, but the 570 will be getting an aftermarket GPU cooler soon, so it should just be drive noise soon. Point is that you don't need to have an expensive case to have one that is effective, and a little stylish. Cooler Master Elite cases are also in this price range and I have heard good things about them.
Well, that leaves you $45 on your budget, so you will have to go a little over to get a good GPU. I would suggest waiting until the 7770 and 7750 come out and get one of them, or else wait for the 600 series by nVidia to be released soon.