Dude, open ended question
What vid card do you have now?
What mobo/cpu do you have now?
How much money are you willing to spend?
Does your current vid card run all your games well?
I would say that if you have a GF3/radeon8500 now you can afford to wait. If you don't have a DDR/Rambus system I wouldn't waste cash on a GF4 or GF3, I'd get a new mobo/CPU/RAM. If price is an issue look at a GF3 (almost certain to drop in price) or a 8500.
And lastly, something that many people forget: if what you got right now works great, don't spend money on the new thing. There are like 3 games that take advantage of the GF3 and it's been out a year. The same thing will happen to the GF4