I don't think there's been any official statement on this yet, but for quite some time it's been thought that most likely the '05's will come out in or around September '04.
Waiting on buying an '04 might give you more leverage in negotiation; most people seem to be assuming this, and I think it's usually true. But -- beware! -- I don't think it's necessarily so. For example, suppose there are hardly any '04's left, and that there are a lot of people like you who've been holding off lately, under the assumption that the deals will be better. What you have is a supply-demand situation working totally against you. The deals might not be better; in fact, you might not even be able to get the car.
And if you suppose also that the prices of the '05's will be at least a few hundred dollars higher (which I think is likely although most other people seem to disagree), then you might REALLY have a high demand for those remaining '04's.
Cliff's Notes: The deals usually are better when the next year model comes out. But don't count on it.