My rig cost about 1 grand, but I overpaid for a couple of my components. If you really watch the deals, you can probably put something together for like $850 ish, maybe $900, that would be EXTREMELY capable. Fry's had the i5 2500k on a big sale about a week ago. I think it was $179.99 or something like that. I was surprised to see it so low, I think it was $10 cheaper than I've ever seen Microcenter have it. I also saw a good deal somewhere on an Asus P8P67 Pro for even cheaper than the regular one that I got. I've seen decent versions of the GTX 560 Ti for as low as $189.99 after rebate. They key thing is getting all the right parts at their lowest possible price. It's really all about patience.
Here are some parts from my rig that I would definitely recommend, and what I paid for them:
CPU = Intel Core i5-2500K
3.3 GHz (3.7 GHz Turbo), Quad Core, 6 MB L3 Cache ($196.64 with tax, on sale at MicroCenter)
You might be able to find it for $179.99 at Fry's.
Motherboard = P8P67 R3 LGA 1155 P67 ATX Intel Motherboard ($152.94 with tax at MicroCenter)
I definitely overpayed for this motherboard. I should have gotten the Pro version of this motherboard for the same price. Right now, you might be able to get the regular version for $130 shipped, maybe even a bit cheaper. Just make sure you never want to crossfire or SLI. If you want to do that, then pay more for the Pro or Deluxe versions.
Memory = G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-8GBXL----------- $69.00 shipped, after tax (newegg)
Basically, make sure to 8 gigs, and make sure it's DDR3 1600. You should pay $70 or less shipped.
Power Supply = SeaSonic S12II 520 Bronze 520W ATX12V V2.3 / EPS 12V V2.91 80 PLUS BRONZE Certified Active PFC Power Supply ($74.59 shipped, after tax and shipping , Newegg)
I spent $75 on a PSU, but I got a damn good one. Quality PSU's cost money. Mine is only 520 watts, but very effecient 520 watts. Yes, I wouldn't want to Crossfire or SLI with only 520 watts, so there is that to consider. If you need to crossfire or SLI, then you need to go like 850 watts to be on the safe side.
Hard Drive = Samsung SpinPoint F3 Desktop Class 1 TB ($54.07 Newegg)
SpinPoint F3 is very well known and respected HDD. Sometimes you can find it for like $48 shipped.
Case = Antec Three Hundred Black Steel ATX Mid Tower - ($54.07 / 39.07 Newegg)
If I ever get my rebate back, then I'll have got this for $39.07 shipped, which isn't bad at all, considering I have to pay tax for stuff from Newegg. The case does everything I need it to. I did add some extra fans to it, raising the cost up slightly, but it's all gravy.
CPU Cooler = Cooler Master Hyper 212+ ($23.05 after rebate $33.05 before rebate - Frys)
I'm still waiting on my rebate for this.
Operating System =Windows 7 Professional 64-bit (Student upgrade version) $30 (Digital River via download)
You just need to have a .edu email address (or find a friend that has one), and then you can download it for $30.
As for the GPU, right now I like the 560 Ti for around $190 ish after rebates. The key is getting a dual-fan version of the card, and not a single fan version. Also, make sure it's a reliable company and it has gotten a decent review. I way overpaid for mine, but I just got tired of waiting for a sale, and just said F it. I was waiting around with all the parts except the GPU, so I finally just bit the bullet. Had a waited just two more weeks, I would have likely saved about $30 or more. Oh well.