My budget is around $1500, but I'm not in a rush to get it. Should I wait for new graphics cards (ie GTX 780 or Radeon 8970), or will the performance boost not be significant enough for the wait? Also, will DDR4 be out relatively soon?
DDR4 will not be out for at least 3 years, in the consumer market, at least.
The 780, if the rumored specs are true, will be one hell of a GPU. It is practically going to be a better 7970; 3GB VRAM, but lots-o-CUDA cores. Is it worth the wait? Probably not. Just get a 7970 now and be happy. They beat 680s, and are great for both gaming and editing (OpenCL). Get some fast DDR3 (2133mHz CL9/10) and you'll be fine.
Thanks for the feedback.
Even the lastest titan card isn't making big waves over the current 600 series nvidia cards. The price points for AMD are tonnes better for the cards you can afford. 680s are like 400-600 dollars while the 78xx radeons are 200-400 And by logans bench tests the AMD is almost on par with nvidia for the most part. I would concurr with bren there get a sweet rig for 1500 now and it'll be good for the future.
Just a little note future proof your PSU get this one... http://pcpartpicker.com/part/corsair-power-supply-cx750