2x Gigabyte Radeon HD 7870 OC GHz Edition - $270

The full part number is: GV-R787OC-2GD. You can find an Amazon listing here: http://www.amazon.com/gp/product/B007PJVB3Y

I've had these cards in my computer for about two years. They are real workhorses and play any game at 2K up to high. If you're into that, you can overclock these cards pretty heavily. They struggle with higher levels of AA, but they will play pretty much anything on the market today at high resolution. They are designed to run in crossfire and you end up getting about 1.6x boost having two cards.

If you are interested in netsec, these cards were really popular a year or two back because they have an incredible hashrate, even when used in conjunction. I personally never mined with them, but I've cracked a few passwords and can vouch for their speed.

I'm thinking about getting rid of them to subsidize a nicer Nvidia card because having two cards is not as much of a benefit as I thought it would be, and I don't do any serious hashing anymore. If you are looking to build or upgrade a PC, you can buy two of these for amount I paid for one, $270. For $300, I'll install them for you.

Some things that they are finnicky about:
They are large cards, so you won't be able to fit them into a microATX configuration or a smaller case.
You'll need a decent amount of power. They are factory overclocked at 1100 Mhz and are stable. I have them at 1200 Mhz on a 750Watt PSU, which may be a bit excessive but I have never had power issues.
They will blue screen sometimes, especially if you don't keep the drivers up to date. That's just one drawback of having twin cards. Sometimes you have to do a bit of googling to optimize the crossfire profiles for the cards.

I'm not set on selling so my price is pretty firm. Used cards are selling for $160 each online, so I figure $135 each and in person delivery makes it fair.

As a side note, if you are looking for someone to build you a computer, I can do that too. I charge 10-15% depending on the scale of the build. Contact me if interested.