For twin GFX, < $200 each I'd go with the two 6870's .... at > $200 each, the 900 Mhz 560 Ti's give most performance per dollar. Guru3D uses the following games in their test suite, COD-MW, Bad Company 2, Dirt 2, Far Cry 2, Metro 2033, Dawn of Discovery, Crysis Warhead. Total fps (summing fps in each game @ 1920 x 1200) for the various options in parenthesis (single card / SL or CF) are tabulated below along with their cost in dollars per frame single card - CF or SLI:
You should stick with the Sandy Bridge , The card manufacturers all will use the same gpu and they can only tweak a few things so they will all be in the same ares for performance , one may come overclocked a little higher than the other from the factory but you would have to go up or down levels to see noticeable differences.
I would go with the Asrock board , more slots , same features less money.
Since you are planning on Crossfire in the future then you should get a psu to support that.
The 2500K will trounce the Phenom all day long, but the Phenom is still a good chip, and cost's a little less if you need to make room in the budget.
Cannot comment on the GPU as I don't know much about AMD boards. However, I would go with an AMD unless you are using CUDA, Physx, or using a high end card.
Just stick with the SSD for now, and get a larger one. HDDs are ridiculously overpriced right now, and if you can hold out on storing any bulk information then you should be able to snag a 2+TB drive next summer/fall for under $100. Besides SSD's are at a decent price right now, and really make the system feel very fast and fluid.
CD, just get the cheapest DVD burner you can find, unless you want blueray support, in which case you should get the cheapest blue ray player/DVD burner you can find.
Motherboards are tricky things. I purchased the extreme3 gen3, and was happy with it until I started having RAM issues (turned out to be both bad ram, and mobo issues), but I am sure it is a fluke. However, I feel that I should have stuck with the p67 chipset on an MSI military class board as I am now not going to be using the SSD cashing, or the Virtue/igp video rendering options (found there was a huge performance hit and ram usage with Virtue... but perhaps the performance hit was due to the bad mobo? I can eat the ram as I have 16GB). Anywho, the only other reason to get the z68 is for future Ivy bridge support, but if you buy an i5K, then I dobut you will want to buy the next gen i5K unless something goes terribly wrong... in which case you would likely buy a who new mobo anyways as the CPU will survive almost any catastrophe. Besides, as the writers on Toms and other sites have already hinted, the z68/IB combo may not be quite as good as we have been lead to believe. However, if you have your heart set on a z68 board then I am sure any of the above would do just fine... just know that you are not getting any extra speed over a p67 board, just extra features.
For the PSU I really like my OCZ ZS I got. Great rebate made it $75 for a good quality 750W power supply. Only complaint is that it is not modular, but as I have never had one, so I dont miss it that badly.
For the case I suggest looking at thermaltake for good budget cases, Cooler Master for their HAF and upper end jobs, and LanLi, Corsair and other good name brands for ones that have a more interesting look/feel to them.