Wii sales will not drop off much at all at any point next year and will completely dominate the first half of 08, due to incredibly strong sales of Wii Fit, SSBB and No More Heros (to a lesser extent) and strength of the Nintendo brand (the reputation that Wii and DS are far and away the most fun systems) and the appeal to nearly all demographics.
Wii Fit will start with sales of ~100,000 in USA/Canada, leading most people here to proclaim it a flop, only to sell nearly the same amount EVERY week throughout the year.
Mario and Sonic at the Olympics will be one of the largest sellers next year in all territories.
By the end of the year, the Wii will have outsold the NES worldwide and a lot of people here will feel silly for doubting John Lucas.
360 sales will stay steady throughout 08, because the biggest game of the year (GTA4) is coming out during a typically slow season and there will likely be another price cut in the US and Europe. Japanese sales=dead.
GTA4 sales for XBox 360 vs. PS3 will be at a ratio of 4:1 in favor of the Xbox 360.
KillZone 2 will be the Lair of 2008.
Metal Solid Gear 4 will between 600k and 800k by the end of the year and go down as the biggest flop in gaming since ET for the Atari 2600 back in 1983 (Due to its extremely high production costs) This will be a devastating blow to Konami and to Sony, who will see developers cancel projects and move them to other consoles.