I don't think price is going to be as big of a factor as people think it is. The demographic the companies have been aiming for has been the 18-35 age, and $500-600 for a system really isn't that bad... especially from what we saw last holiday with the 360s on ebay. They'll sell their units, it'll simply mean people will buy them from the store for retail price rather than on ebay for inflated prices. What's the point in selling it for $400 like the 360, lose tremendous profits, to only have a supply issue and have ebayers make all the money.
Then a year later (1.5yrs from now), when more people have HDTVs (i think it's safe to say that the majority of people who buy TVs now are buying HDTVs), and the PS3 drops in price, more people will buy the system.
So my prediction is that the PS3 will be on top still. They've been dominating the market since the PS1, and a lot of those PS1 and PS2 players are now adults in the 20s, who can afford $600 for a system. They're also the generation who are technologically minded, so HDTVs and high tech toys are the norm for them. They're use to paying hundreds of dollars for a video card, cellphone, PDAs, computers that need upgrading every year or 2, etc, etc.
The 360 will eat a big chunk out of the PS3 market though, simply because they've had a year start and because it's so significantly cheaper... and there's a good chance the price will probably drop by another $100 or so to compete with the PS3.
As for the Wii... now that's a good question. I think consoles are one of those things that won't do good simply because of a cheaper price. Gaming has a stigma of being immature entertainment, and both teenagers and adults don't want to think they're playing with a kids toy. Yeah yeah, some of you guys are going to say you don't care what people think of you, but this is going to affect the sales. The name, the controller, much of the games, and even the price, all points to this being targetted at kids.
Like it or not, consoles have become a sort of status or luxury symbol (amongst gamers at least). So my prediction is that the Wii comes in a distant third again.