I think there are a lot of potential candidates. Some will be more mid-card and tag team guys but I think WWE will put a few main eventers in the running, or at least into the MITB matches themselves, to add some star power to them. In no particular order:
Randy Orton
Sheamus
Cody Rhodes
Antonio Cesaro
Damien Sandow
Daniel Bryan
Chris Jericho
Dean Ambrose
Seth Rollins
Mark Henry
Fandango
Wade Barrett
Kofi Kingston
When it comes to the SD! MITB case, it's pretty wide open. I don't see Orton or Sheamus picking up the WHC MITB briefcase. I could see them in the WWE Championship MITB match easily. If Ryback winds up winning the title in the near future, I can easily see WWE building Orton or Sheamus as top contenders for the strap.
I don't think Fandango is a realistic possibility at this time, but it'll surprise me if he's not at least in the WHC MITB match. He's getting good responses and Vince is said to really like the character.
Chris Jericho probably isn't a likely candidate either but he can add a lot of quality to any match he's in. Jericho is known to be extremely unselfish and it seems that he's enjoying himself putting over young talent at the moment. Given his part time schedule and various other interests he has going outside of wrestling, it's a great use for his ability and star power.
Cody Rhodes seems like someone who is ready to be elevated. He's been in the mid-card & tag team scenes for several years and it just seems like he's in a right spot to get the briefcase.
Wade Barrett is a guy that probably would already be WHC if he hadn't gotten injured last year. Instead of WWE building him back up with a strong mid-card title run, unfortunately, he's been pretty much buried over the course of the past 3 or 4 months. Still, it wouldn't surprise me to see Barrett get the spot. He's got the ability, he just needs to be given a consistent push without Vince losing interest smack in the middle of it.
Daniel Bryan is a real possibility as well to win MITB in my opinion. He's consistently shown himself to be one of the most over wrestlers on the roster and is able to get fans rallying behind him. If he doesn't go into the hunt for either the IC or US titles, in which case I hope & pray that he gets a strong run, I see him in the WHC hunt either as a direct challenger to Dolph Ziggler or as a strong candidate to win MITB.
Ambrose & Rollins are both on a major push as part of The Shield right now. I don't think either of them will be Mr. Money in the Bank this year, but I can honestly see one of them in either the WHC or WWE Championship MITB match. Personally though, I see Rollins & Reigns as tag champs and Ambrose as US champ before long. As Ambrose has gotten the singles matches thus far, I think he'll definitely be in one of the MITB matches at least.
Antonio Cesaro is extremely talented and another solid candidate for Mr. Money in the Bank. Cesaro did a good job as US champ when you take into account how limited his character was. Like Barrett, it's a shame that he was buried during WM season. He's tied with Shelton Benjamin as the 7th longest reigning US champ in the history of the title. The past couple of weeks on Main Event, Cesaro has looked like a true star when putting on two killer, ppv worth matches against Kofi Kingston & Randy Orton. I'm not sure that he'll win it, but he's someone that should be considered.
Damien Sandow is a great all around package. He has a decent look, he's great on the mic, he's very comfortable in his character and can go in the ring. I think there's still a lot of untapped potential in Damien Sandow and I hope that WWE simply doesn't waste the guy. I don't think he's too likely to win MITB, but I do see him in the WHC MITB match at least.
Mark Henry is someone that seems to be an almost different wrestler. Two summers ago, I'd have laughed at anyone who said that Mark Henry had what it took. However, Henry has been constantly entertaining since the summer of 2011. He's been extremely believable as a monster heel and he's gotten the best booking of his career. Henry is someone that's been in several MITB matches and he's there to be the human juggernaut. I see him being in one of the matches, but I don't see him winning.
Kofi Kingston is someone that, in my opinion, has a lot of potential that remains untapped. He's a great mid-card babyface that has always gotten solid responses from the fans and his matches are often among the best on the card. I honestly do think that Kofi has ability that we haven't fully seen yet and MITB could be what gets him over the hump.
As of right now, I think it's just too close to call. I'd say my favorites for being Mr. Money in the Bank at this point are Cody Rhodes, Wade Barrett and Daniel Bryan.