You could wait, but if you're in the market for a ~$150 card a GTX 260 or 4870 would not be a bad way to go. The new cards (5850 and 5870) from ATI are probably going to be double that or more, so they will be out of your range. Also, I honestly don't see the current gen cards dropping too much more in the near future. It makes sense that $300-500 cards drop when a new generation launches, but the cards are so low already I just don't see them dropping significantly until there is a next generation card in the $150 price range the solidly out performs the GTX 260.
...it really comes down to how urgently you want the card. Waiting will always get you the same or better for less money, but IMO 2-4 months of better performance with a new card has value as well. Although, I'd shop around for a better deal then Best Buy.