Video card selection for new gaming system

I'm in the market for a new system that will be primarily used for gaming. Originally I had planned on going with a resolution of 1920x1200, however I've realized that with my component set and price range I might have to settle for 1680x1050. That is why I have come here, to get some help from you guys!

The following are the components I've decided to pick for my new system (minus the video card, that's why I'm here). I'm looking for something that is pretty future-proof for quite a while as well. Of course any suggestions to modify these are welcome as well (keep in mind all prices are listed in Canadian dollars):

Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor $202.99
GIGABYTE GA-EP45-UD3P LGA 775 Intel P45 ATX Intel Motherboard $159.99
G.SKILL PI Black 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory $68.04
CORSAIR CMPSU-750TX 750W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply $159.99
Western Digital Caviar Black WD6401AALS 640GB 7200 RPM 32MB Cache SATA 3.0Gb/s Hard Drive $98.49
LG Black 22X (CAV) DVD+R 8X DVD+RW 16X DVD+R DL 22X (CAV) DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 22X DVD±R DVD Burner $29.99
XIGMATEK HDT-S1283 120mm Rifle CPU Cooler $45.99
COOLER MASTER RC-690-KKN1-GP Black SECC/ ABS ATX Mid Tower Computer Case $98.69
Microsoft Windows Vista Home Premium SP1 64-bit for System Builders $149.99

This totals to $1014.16, which is probably more than I'd like to spend on a system without a video card. Next, of course, I need a GPU. I have a couple selected already that I thought might fit in with the rest of my components:

XFX GX260NADBF GeForce GTX 260 Black Edition Core 216 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card $307.84
XFX HD-487A-ZDDC Radeon HD 4870 XXX 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Low Profile Video Card $338.24
SAPPHIRE 100270SR Radeon HD 4850 X2 2GB 512-bit (256-bit x 2) GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card $381.69
SAPPHIRE 100251SR Radeon HD 4870 X2 2GB 512-bit (256-bit x 2) GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card $528.09

With the first three cards listed, after taxes and shipping, I'm looking at around $1,600. This is pretty much the max amount I'm wanting to spend on a system, and this is still stretching it pretty high. Originally I had planned for a system around $1,000-$1,250, taxes and shipping included, but it seems that where my sights are this just isn't possible. Let's also keep in mind I need to get a monitor on top of all of this!

I'm also open to the idea of getting an SLI or CrossFire motherboard, although at the moment I'm set on a single-GPU configuration, as it seems a lot more cost effective.

Well if you don't mind spending that 150$ more, you can buy the 4870x2.
But price/performance ratio, the 4850x2's more worth buying though, IMO.

I find it hard to believe you are spending that much on a mobo and dual core cpu when you could have a fast quad core for the same amount of money.
Socket 775 is dead, what are you going to upgrade to later?? Your only choice would be a QXXX -OR- you will have to buy a new mobo, cpu, and ram later. Is this dead end really a good investment?

Are you suggesting a Core i7 setup? It would be nice, since I wouldn't be backing myself in a corner upgrade-wise, but the amount of money to go this route is through the roof. I'm really looking at getting something soon, however maybe for what I want I will have to wait another couple of months.

Not bad but I would make a few changes

Here all prices are from www.newegg.com in "bold" are my recommendation.
Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor $202.99
Intel Core 2 Quad Q8300 2.5GHz LGA 775 95W Quad-Core Processor Model BX80580Q8300 - $189.99
GIGABYTE GA-EP45-UD3P LGA 775 Intel P45 ATX Intel Motherboard $159.99
(good board I've got a P31) (Currently $134.99 at newegg)
G.SKILL PI Black 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory $68.04
Kingston HyperX 2GB 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) $23.99x2 (47.98)
CORSAIR CMPSU-750TX 750W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply $159.99 ($129.99)
Western Digital Caviar Black WD6401AALS 640GB 7200 RPM 32MB Cache SATA 3.0Gb/s Hard Drive $98.49 (Currently $74.99)
LG Black 22X (CAV) DVD+R 8X DVD+RW 16X DVD+R DL 22X (CAV) DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 22X DVD±R DVD Burner $29.99
XIGMATEK HDT-S1283 120mm Rifle CPU Cooler $45.99
COOLER MASTER RC-690-KKN1-GP Black SECC/ ABS ATX Mid Tower Computer Case $98.69
Microsoft Windows Vista Home Premium SP1 64-bit for System Builders $149.99

As for video card depending on what you want to play I for see two options. If you like ATI (I'm not a fan personally) 4870 or 4870x2 are great cards in performance (I don't like ati drivers) and there are some good open box deals on newegg as of late. For Nvida if you want budget get 9800GT or 9800GTX they can be had from $120-$170. If you want something that will play crisys well I just got yesterday (open box GTX260 $157), go with the GTX 260 or higher but be warned that the 9800GTX and GTX2** series cards are 10.5 to 11.5 long. Newegg has a msi GTX 260 for $215 which just came down was $249 plus a rebate available.
My system
E7200 2.5GHz Core 2 Duo
4GB Kingston HyperX DDR2 1066
Seagate 640GB 32mb cache 7200rpm
MSI GTX260 896mb

I can play crisys warhead at max setting with 4xAA, on 1280x1040 flawless. I've not tried to add higher AA yet. I can also play original crisys on high with 4xAA on 1280x1040 really well. All non-overclocked from mfg settings.