If the question is the GTX 560 and GTX 560 ti the answer is probably yes, but only as a dual GTX 560. I have read that the GTX 470 and GTX 480 can be SLI'd, but with the limitation that it can only be SLI'd at the lesser of the two cards.
The core counts of the cards you mention are all different from each other and as such the pairings won't work.
You could run the GTS 250 and the 9800GTX+ in SLi.
So long as the VRAM sizes are the same.