Well your options are if you can wait or not. Next gen cards are speculating between 15-25% performance boost and the big deal is it will take 50% less power consumption to produce it.
They have been delayed due to slow production of 28nm chips to both AMD and Nvidia. AMD is going to be cutting some corners to get it out but no set date yet. Your looking at late December absolute best and most likely with AMD only. Realistically January for Nvidia.
Big question is for that extra performance and lower power consumption will it be as over clockable and will it be able to handle any extra voltage? It's all speculation of course. It may end up not being that much better than current cards where most of them can be heavily over clocked or even unlockable shaders etc...
Now the normal upgrade progression is if your in current cards now, when next gen cards come out, you SLI/Crossfire your current gen card. Get more performance as opposed to buying a single new gen card, if your on a budget.
If your in last years cards 400/5000 series, and you can wait till next gen, then you'll buy one now and double up when the following gen comes out after next gen. Etc.....
Example - Let's say you have a 560Ti/6950 now, would it be more wise to get a single next gen 660/7950 card? or double up and SLI/Crossfire your current card? For the most performance boost one would double up on current gen card.
So if you should decide to buy one now, I'm going to bet your not going to buy a single next gen cards in a few months. It wouldn't be the end of the world because your still going to have one rocking system SLI/Crossfire anyway down the road.
So logically, it's up to you if you can wait.
I'd stay away from buying a second GTX 460 for $150 right now and then have to put down more money later IMO.