At 1920x1080 I'd suggest doing SLI GTX 460 1GB. The 768MB version is going to limit you at that high of a resolution. So I'd disqualify that one to be honest.
Also, an SLI GTX 460 1GB setup will perform about 20% faster than a GTX 480. And the GTX 480 outperforms an ATI 5870. So with those three options, the SLI GTX460 1GB setup is the best performing option.
If you can afford to do it, either go for SLI 460 1GB, or get a 5870/GTX 480 in some benchmarks. The GTX460 768MB isn't a great idea.
Now, on the other hand. Pricing on the GTX 470 is coming down pretty quickly. And a single GTX 470 performs pretty well @ 1920x1080 by itself with most games. However, it will run louder & hotter than a couple GTX 460's. So you have to weigh out pricing. SLI 460's is more performance than you need (which is good long term), but a GTX 470 is probably plenty for now.