If you're aiming for a "top of the level" rig (which it seems you are), and you're not willing to wait for the GTX 6xx cards, I suggest you get two GTX 580 3 GB and put them in SLI mode. You'll have even more power with them than with a single GTX 590 (especially with fabric overclocked GTX 580....the difference in the GPU core frequency can reach up to 300 mhz PER CARD, compared with the GTX 590). Plus, you'll have double the vRAM that way.
In any case, anything you choose will be clearly overpowered for Skyrim.
Thanks for the quick answer!
I was hoping to avoid the hassle with SLI mode (eg. getting a fat power supply, some games not supporting more than one card, cooling issues etc etc), so it's really just a matter of those three cards.
The annoying thing is that I prefer the Asus cards, but they have yet to announce a 3GB version of the 580...
Also, I am not aiming for a "top of the level" rig unless I have to. Skyrim is my main concern. I want to max it out on a 1920x1080 screen and a have a good framerate without stutters. If a 1.5 GB Gtx580 will suffice for that, it'll probably be the way to go, if it cannot be fully guaranteed to do so, I'll likely go for a 590 (which in sweden isn't that overpriced in comparison (4000 sek vs 5700 sek).
I'll just assume Skyrim will have multi-gpu support.