Well, let's take a look at the teams.
SA, TR, Spyker are, well, themselves. Won't challenge at all.
Williams and Toyota were unimpressive in 06. I don't think 2007 will be very much different. Williams might be able to do something with Rosberg and Wurz, who appear to be good.
Red Bull will probably have a good car, between their new engine and Newey working on the car in the off season. The men controlling the cars might hold them back. At Mclaren, DC was usually pretty far behind Kimi. Webber is pretty old. Not sure what he can do.
BMW Sauber have proven to be very quick in 2006. I would assume them to remain about the same in 2007, consistently finishing in the points, but not being a huge factor in the championship. Expect a challenge, though. May be similar to Honda of 06. A win wouldn't be too suprising.
Insert Toyota here if for 2007 they put thier fatty budget to good use.
Honda have picked up the pace toward the end of 06. However, their last "greatness," 2005 was the result of "cheating." I'd expect a win or two, but not a championshp from these guys. I do feel that the drivers could be very qualified though. Both had a decently qualified season in 2006.
Renault will miss Alonso. Fisi was consistently behind Alonso, although he did have a win. Kovalainen could either be a God or just suck. I'd expect him to follow the finnish tradition of being good from the start. He'll probably give Fisi a run for his $. This team did win the chanpionsip in the 1st half of the season with an illegal mass damper. These guys wil probably pale compared to the big guns at McLaren and Ferrari.
Don't expect McLaren to have a very good season. I don't think the car is very fast, although I am a fan. Personally, I think Kimi was just good enough to make the car competitive. (notice how the 2nd driver was never nearly as good as Kimi?) They will miss Newey, so the car should deteriorate a little further. Alonso's skill, however, sould do similar things compared to Kimi's. With the fate of other teams, Mclaren should be more competitive (maybe a win or two?).
Lastly, I think Ferrari will reassume the top step on the championship. Like other teams, they will miss their big hitters @ the top. I don't think they will fall very fast. (give 'em a few seasons). Kimi and Massa are good drivers. If Massa isn't, then the strength of the Ferrari was proven by his poles and Kimi will be uncontested in 2007. Ferrari's reliability will be key too. Kimi's luck, however, could follow him or it could me Mclaren, in which Alonso would see some bad times.
Here's the bias: I tried to give teams an equalish view in my mind. I am a die hard Mclaren and Kimi fan. It will be tough deciding what manufacturer to go with in 2007 (Kimi's red or Alonso's McLaren.) I also like Button. I honest;y don't really like Ferrari or Alonso, mostly because they are/were Kimi's main rivals at one point.
Error: Expect a lot of error from me. I generally get wierd ideas and follow them passionatly. I think my opinion is good to within +/- 15%. My comparison might also not be the best, going mainly off 06 events. Any team could do an 05 Ferrari or 2006.5 Sauber. As was said earlier, we'll see next spring.
GO KIMI!!!