Kind of incomplete, as youve not mentioned what you currently have, what games you want to play/are playing, and what card/s youll want now.
If you want DX11 now, youll have to buy ATI.
If you want to wait for nVidias solution, youll have to wait at least another month or 2.
If you buy a card now, I can say, some are overpriced for what you can get than by going ATI, plus youd have DX11.
We need more info from you
Well if you wait until you are sure that nothing will come out that is faster or cheaper in at least the next 3 months, you will die before getting anything. Pre Xmas is always a bad time to buy GFX....new generation cards come out in the Fall.....those get continually improved and new versions come out till June and then we all wait till it all starts over again in September.
If you **need** a card, get one .... what one you get will depend on your needs and budget. Good place to start is here:
What makes it a very "weird" time to buy is in that article you'll see that the best cards for the money are "old" cards in 8/10 cases. IIRC, from the $150 and up category, ATI's older 4xx series took 6 wins, while ATI's new 5xx series too just 2 wins and 2 honorable mentions, and nVidia's old cards took 2 wins and 1 honorable mention.
By late February (my guestimate), ATI will have better drivers for the 5xxx series, the individual manufacturers will have progressed beyond reference designs and nVidia will passed the initial release stage w/ Fermi cards.
IMHO, id wait, if you can, for the second or even third gen of DX11 card, let them grow into themselfs for a bit, and actually let some games companys bring some worthwhile titles out, so they too can be at least sure of thier programming!
Whatever fits your budget and if you really care about DX11.
I bought a HD 5850 and stuck it in my PC with WinXP. Why did I upgrade? My X1900XT died. Will I upgrade to Win 7? Yes, eventually, but WinXP serves my needs still and paying $185 for Home Premium (retail) is not worth it just to see DX10/11 graphics for the moment. Probably next year.