With a $1200 budget, you can get a pretty serious gaming and editing rig. Here's my suggestion:
CPU: if youre not doing some really serious editing, go with a i5 3570K. Its about $210 and gaming wise this will be everything you need. If you want to go enthusiast on this rig, spend some extra money on a i7 3770k. Its about $100 more but it will perfom better editing - again, we're talking about serious editing. If your graphics design isnt something professional, stick with the i5 and you'll be just fine.
CPU cooler: I'm a endorser of Corsairs Hydro Series. I'd go with either H55 or H60 or H80 depending on how much money you have left. Around $50- 80
Mobo: Get any Z77 chipset from reliable brands such as Asus, ASRock, Gigabyte. Here you can choose acording to your needs - Number of SATA ports, USB 3.0, Memory Standard. I'd go with ASRock Z77 Extreme 6. Beautiful board, USB 3,0, 4x SATA 6gbs and stupid fast memory standard. Around $150
Memory: Get either 2 8GB DIMMS. Either good overclockable 1600Mhz or just stock 1866. I'd go with Corsairs Vengence 16Gb 1866 kit. Around $80
GPU: Since you be editing and designing i'd stick with Nvidia since they have CUDA. Go with some overclocked edition of the GTX 670. You can find various prices here. I recently bought a EVGA FTW+ GTX 670 4GB for $430. Amazing GPU, extra GDDR will certainly improve editing performance.
PSU: Get any reliable brand with 80 PLUS Bronze certificate with 750W. Id go with Corsairs CX750. $65
Storage: 1x 128GB SSD (around $120) for OS + 1x 7200RPM 6gbs HDD for storage (get any size u'd like, prices vary alot. A Seagate 1.5TB is around $65
Case: Get any case you'd like with good airflow and cable management. You can get pretty good ones at $100
This rig sums up at around $1230. If you have money laying around and really wants to go enthusiast ( spend more money at little performance gain just to the get best of the best) , you could: get the i7 over the i5; get an GTX 680 over the 670; get an extra pair of DIMMS; Buy a enthusiast Mobo; get an Corsair H100. Or any combination of these modifications.
Good luck with ur Rig!