Hello,
Budget, yeap I should of mentioned that. My last system was in the 5K range and that is for all hardware and O/S's, so it is not so much of a budget. That is also very flexible but will be kept sensible.
I would like a pair of 780's or what ever is about when I build, but I also have to think about space and other boards.
Also, as this does effect what is available, I am now in the UK not the USA. Some thing are not available in the UK same as the USA.
Just a few other basics that might be important.
Case, big, black, nice clear side, lights blue.
It goes without saying, but will just in case, must be OC'ble, even if I don't. I tend too under clock a little for better stability and longer life.
My last system had 2 extra panels on the front, one for the Creative Labs sound card, I/O's and knobs and a second with fan control over rides, nice digital display with temps.
Have not decided about cooling yet, options are 1 - standard fans, 2 - CPU liquid cooled the rest standard fans, 3 - everything liquid cooled.
Have also run one system with 2 PSU's. 1 was for the mother board and the other for the mechanical devices ( fans and drives ).
Steve
5K? Holy hell you can build one badass computer for that.

PC hardware changes all the time, but pretty much you'll just be looking at the latest Intel CPUs and Nvidia GPUS (unless AMD ever gets the price down on their GPUs). All of the high end Intel CPUs are normally very overclockable (the K models) but it would b ebest to look into that as I don't normally follow the overclocking scene.
GPU
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487003I wholly recommend EVGA for Nvidia GPUs. Best customer service I've ever dealt with next to Amazon.
Have you ever SLI'd GPU before? They cna be a headache I hear. Games may not support SLI all that well and stuttering can occur. However, you can max any game with a single GTX 780 Ti alone so you wouldn't have to worry about that.
CPU
Like I said, any high end Intel CPU would be good. Their top CPUs are 6 cores, but cost over $1,000.
Motherboards are a bit trickier to pick the best one. It all comes down to preferences. I've only used Gigabyte mobos and they've served me well. I've heard EVGA and Asrock makes good mobos too but I haven't really looked into them much.
RAM
Without a budget you can probably go for 16gb of 1600 ram. You can get faster ram, but there really ins't much point in doing it.
What exactly is your PC going to be used for? If it's just gaming you could probably scale back a ton of uneeded stuff. Why spend more money than you need, right?