Platypus helped me with a build that worked out perfectly.
I upgraded from a:
AMD Athlon II X4 3.0GHz Quad Core - ATI Radeon 57701GB - 6GB DDR2 - 550W PSU - 500GB 7200RPM HDD
(Was up and down frames wise for TF2 on low settings, other games on low)
To a:
Intel i5 3.2GHz Quad Core - GeForce GTX 7702GB - 8GB DDR3 - 650W PSU - 256GB SSD - 1TB 7200RPM HDD
(Maxes out on every single game without any drop in performance)
The difference is astronomical. Everything is much faster and the most important difference to me at least was getting the SSD. In the end with tax and all it ran me a pretty penny of almost $1400 but it was well worth it. Now I won't need to upgrade for a few years and it's a solid build. You should go for the 770 if it's only like $70 more. The case should just be something easy to use build wise. I went with a Corsair 400R? The PSU I got was probably not necessary but I can re-use it in the future since it was a quality one. You won't need the after market HSF most likely as everyone says the stock intel ones are good. Everyone I spoke to told me the i7's performance over the i5 was negligible and wasn't worth the extra $100. In the future though if I need to upgrade that it shouldn't be too difficult to do so which is what I wanted. A base that I can work with which is important.
This is the full build platypus put together for me: http://pcpartpicker.com/p/3yz0v
I had to change a few minor things because I drove straight to microcenter and bought everything in person so I didn't have to wait (changed minor stuff depending on what they had in stock, just the case rly) then I stopped by solidsnakes house on the way home to get help putting it together. I changed the case, added an optical drive (make sure they send you the L sata cable bc mine didn't come with one from microcenter for the $16.99 LG one, came in a clear plastic baggy with no box and no cable), and I also had to buy another Windows 7 Home OEM bc I can't be bothered with pirating it i'd rather just spend the $100 just in case anything ever happens it's easier to deal with. I'll give my old copy to my fiancee along with my old computer.
After a few weeks of having it now the only things I might consider doing on my new rig is adding another 8gb of ram and possibly getting a bulky HSF if I want to try and overclock which I think I should be able to achieve with the right guidance because I admit I have no idea how to do it and it scares the shit out of me when your screen crashes after trying lol.. The processor is incredibly fast though on its own so I don't know if overclocking is really necessary.
Edit: As far as monitors go, I bought a BenQ XL2420T 120Hz 24" LED about a year ago and my old computer really didn't show its potential. After getting my new pc up and running you can see a big difference in the 120Hz side of things. It's probably the best gaming monitor you can grab and I bought a refurbished one for about $360 at the time I believe and haven't had any issues. It's a solid piece. I also have the CM QuickFire Storm Cherry small keyboard and I love it although my teammates complain it's a bit loud on mumble.
Anyways, hope this helps.