Right now, I can get my hands on the 2 of the MSI 460GTX Hawk cards for $200 or the MSI Twin Frozr II version of the 560TI for the same price. Of course, the 460GTX gives me 580 performance now, but with the 560TI, I have the option of adding a second card in the future.
As far as gaming platforms, I game on a 1920x1080 ASUS monitor and I play mostly RTS and RPGs. I am not diving into the craziness of the BF3 anticipation.
I would go with the 460's, SLI in the future with a 1GB card won't be that attractive of an option IMO, some games are already using more than that at 1080p and I suspect more will in the future, and there is a pretty huge performance advantage with the 460's over a single 560ti.
460 SLI for sure (as long as your PSU can handle it). Main reason is you dont know if next generation will be better in single card configuration than 2 560 Ti in SLI.
On the other hand you do know now you are getting a good deal on those 2 GPUs.
I do wonder if those are 1 gb or 768mb versions thou.
Personally i have a 560 Ti and im waiting for next generation to know if its worth to even SLI the 560 Ti .
I would go for the single GTX560ti. It will be quieter, generate less heat, and use less power. Not all games run well with SLI, and there is always the microstuttering issue. For your resolution and the games you play, you may even find just one of the GTX460's to be sufficient.
Whichever you choose, make sure your PSU is up to the task; a quality 500W unit will suffice for the GTX560ti, 600W-650W for the pair of GTX460's.
Oh, there's no doubt it's a great deal. I'd only buy the pair if I thought one might be sufficient (check benchmarks; for your games it may well be) allowing you to sell the other. Possible problems with multiple GPUs, especially the microstuttering issue that was recently described in http://www.tomshardware.com/reviews/radeon-geforce-stut... make me reluctant to recommend a pair of GPUs, when a single strong card will have none of those issues. There is also the question of power.
I've had SLI GTX 465s for 11 months and only had the microstutter issue with one game that is over 10 years old and doesn't have an SLI profile. From reading the article it seems to be much worse with radeon's than nvidia cards.