As of today, there are only 4 serious contenders for the AL Cy Young Award. Things can change quickly, of course, and there are several pitchers who would be at the fringes of the debate (C.J. Wilson, John Lester, Carl Pavano) who could theoretically work their way into the debate with multiple shutouts in a row, but it's unlikely.
There are several relievers (closers) who are having great seasons in the AL (Rafael Soriano, Mariano Rivera, Joakim Soria), but the last time an AL reliever won the Cy Young Award was 1992 (Dennis Eckersley), and none of them are dominating enough to be a part of the discussion.
How their team does matters in the MVP discussion, but not in the Cy Young debate, so all of these pitchers have a chance. People differ about how much wins/losses vs. ERA vs. sabermetrics, but Felix Hernandez (11-10, 2.30 ERA, 209 SO) still isn't winning. It's possible to win it with a low win total (Tim Lincecum had 15 wins and Zack Greinke had 16 in 2009), but that seems to be much more likely when there is no 20 game winner (such as in 2009).
It's likely that Sabathia will win 20, and have a decent ERA, probably making him the favorite. Sabathia is also leading all of these contenders in SO (7th in the AL with 170). He also had the best SO/BB ratio (2.58), but it's not extraordinary. Cahill has the best WHIP (1.06 vs. about 1.12 for the other 3). Other factors that might come into play are that Sabathia has already won a Cy Young Award (2007), and Cahill is only 22.
Unless Price or Sabathia have their ERAs skyrocket, it's probably too late for Buchholz or Cahill. They're not going to get close enough to 20 wins to compete with Sabathia, but Price can. Price won his start last night, so that gives him 4 or 5 more starts (probably 4 because the Rays are going to make the playoffs somehow).
In 2007, Sabathia won the Cy Young with 19 wins, while Josh Beckett came in 2nd with 20. Their ERA's were similar, but Sabathia had 40 more innings pitched. Price is 30 innings behind Sabathia, but he ERA is significantly better, which would make it a close call.
One really bad outing can change all of this (10 ER in 2 innings for Sabathia or Price), but barring that, it's shaping up to be a close race to the end. Based on the schedule, it looks like they'll be facing each other in Tampa on the 13th. Another thing to consider is that Sabathia will likely be pitching on the road (he's much better at home), while Price will be pitching at home (8-2, 2.16 ERA at home), which could give Price the advantage.
Clay Buchholz (Red Sox): 15-6, 2.25 ERA
Trevor Cahill (A's): 15-6, 2.72 ERA
David Price (Rays): 17-6, 2.87 ERA
C.C. Sabathia (Yankees): 19-6, 3.14 ERA