Well, I just bought an MSI890GXM-G65 from newegg., it's definately one of the best purchases I've made this year.
I was going to go crossfire, but now I'm thinking to stay with Nvidia because it seems that most of the newer games use Physx; at least the games I like. lol
So, I've never done an SLI hack before, but I'll be getting another GTX 460 soon since they're on sale at Bestbuy.
Also, I'll need a PSU upgrade! If anyone wants to recommend any, I'm looking for +900 watts.
I'm not sure what you mean by 3-4 years though, as PSU wattage doesn't mean anything in terms of longevity, build quality does. Power draw is only going down with newer fab processes coming, so you'll be just fine for the future. I've always had great performance from the Corsair PSU's, I'd go with Corsair or Seasonic.