For $300 you can get an ATI 5850 which is faster than an Nvidia GTX 285 while also costing like ~$70 less
For ~$160 you can get an ATI 5770 and get performance about equal to a GTX 260 if not better once you OC for about ~$40 cheaper...also newer tech and DX11 support
There is no point in getting an current Nvidia GPU right now, they are overpriced and slower than the competition.
If you plan on waiting for the new Fermi GPU's to come out........expect to wait a while as they said they wont come out till ATLEAST March but im pretty sure htey will definitely be delayed a bit again........i also have a feeling they are going to cost a crap load of money as usual, they will no doubt be faster than the ATI 5850/5870 tho but who knows by how much and if its gonna be worth the premium