I didn't read through everything else in the thread so I don't know if anyone mentioned some of this stuff. I'm also looking to build a new desktop (first one in 8 or 9 years now) so I've been doing a lot of research as well. What's I've found is when you're trying to pinch pennies, you have to watch your aggregates. It's easy to say for any given part... it's only $20 more, and it'll future proof me. Add that up across 6-10 components though and it's an easy $120-$200 bucks extra. In addition, the reality is, the future proofing is pretty much hogwash. The extra $200 isn't going to buy you that much more time relative to how fast hardware progresses. Four years from now, your $1000 computer is going to be just as obsolete as your $800 computer. That doesn't mean parts don't matter, but there is definitely a threshold where you cross what is needed to what is just gravy. Build for what you need now and maybe 6 months from now. Don't build for a theoretical game a couple years down the line. If that's what you're waiting for, then just save the money until that theoretical game comes out and build then.
These aren't hard and fast. Take them with a grain of salt, but considering that cost is something that's important, I thought I would bring them up.
1) If you aren't really going to overclock, or if overclocking would just be kind of added bonus, the i5 3750k is overkill and superfluous. You could shave $100 off going with the i3-3220. It's the same mobo so it leaves open an upgrade path all the way to the i7-3770k. If you need a middle ground the i5 3470 is also there at $200. The other thing with overclocking, is you really need a better aftermarket CPU cooler which will set you back another $35-$50.
2) RAM is cheap. But it isn't free. There's no need for 16GB. Save yourself $30-$40 bucks and just get 2x4GB.
3) Motherboard - this is more subjective. There are several Z77 options (leaving open a CPU upgrade to an unlocked i5 3570k or i7 3770k in the future) that are sub $100. It seem like most people have good experiences, but perhaps more frequently deal with issues. If cost is the highest value though, could shave another $30-$40 off here and for the most part just sacrifice some tertiary features (extra ports, extreme overclockability, etc.)
4) The choice of a 7870 I think is good. It's a pretty substantial inflection point in that it's high performance for its cost. Cards costing more than it do not tend to increase performance proportionally to their increase in cost.
Those are my two cents :-D