Definitely wait for HD9000 series.
The HD9970 is out in less than 4 weeks, will be priced at least $100 below the GTX780 and will be a faster card.
Even if you're a Nvidia fanboy, you're still better waiting, because the release of the HD9970 will force Nvidia to drop the price on the 780.
You'd have to be crazy to buy a GTX780 at this point.