gtx460 or gtx460 sli ( difference, if there is ? prices if you know, thanks in advance )
The question isn't for me but I'll answer =P
SLI word means 2(or more) NVidia cards put into the MoBo (it should support SLI, and your power supply should be able to afford the power of two video cards) and connected by SLI bridge, they must be the same cards, let's say GTX 460 in this case.
CrossFire is the same idea, but for the ATI cards.
Regarding the difference, AFAIK (according to tests and benchamrks), it won't double the frames per second (the most important thing in gaming) displayed on monitor ( I'm talking, here, about one monitor. Google "three monitor difference sli" or something like this to find out if it's worth it).
And lastly, price will double for sure =P