The 6870 is certainly a better value right now than the 5870. Sure the GTX 460 is also a good deal, but the 6870 beats it by a good margin so if you have the money go with the 6870. You can wait for the 6900 series cards, but I'm sure that price premium over the 6800 series won't really be worth it, but of course with top end cards it's more about want than need or value
. I say just get the 6870 now.