Brandon Lyon is an easy candidate. I think you have to toss in George Sherrill's name into the hat as he could regress from a rather nice 2007 for him. CJ Wilson is another prime candidate to lose the closing gig but it's really wide open there.
Kevin Gregg falls more or less in the Chad Cordero/Huston Street boat as he could be prime trade bait. Gregg has a fairly good fastball that can see himself through, throws a bit wild, but I think he hangs onto the Marlins' job while the baby fish as they develop as better relievers.
I think Kerry Wood and Rafael Soriano are top 10 material when healthy and usually that's a big if for either of them. Eric Gagne isn't really a high upside man as he's had to take some heat off that fastball, which won't have him posting a gaudy K rate, but as long as his changeup is clicking, he should hold down the job. You can't rule out a possible injury either. BJ Ryan is in the same boat as Gagne. I think his upside is a bit limited in post-TJ like Gagne, but one thing Gagne has over Ryan is a full season relatively unscathed under his belt after having a few corrective elbow surgeries to repair nerve damage.
As for Corpas/Fuentes, one thing Corpas has over Fuentes is that he can keep the ball down with regularity for groundballs, which can be an advantage, pitching a great deal of games in spacious Coors Field.
As for Takashi Saito, he's had the nagging calf and now I believe it's a nagging buttocks that's had him sit out. He looked rusty against the Halos last time out as you'd believe. As long as Saito is about 75-80% healthy, I think the job is still his to lose with all those nagging injuries at his age (if the results are just so-so even), but that could also mean Jonathan Broxton vulturing saves every now and then.