- Face Turns -
The Big Show - He just does not work that well as a monster heel compared to others (Mark Henry), all that 'disrespect' against normal workers seems forced as hell. Also look at him acting out almost crying when he gets, in some way, foiled by Alberto Del Rio. A guy that big does not work as a cowardly, even emotional heel in general. Have him bury the hatchet with ADR at EC and everything's okay.
Brock Lesnar - He's so, so over with the crowd no matter what he does (okay, he was attacking the chairman and the most annoying guy in the WWE so far, so that might be the reason). Since CM Punk vs. Brock Lesnar would be interesting, and CM Punk just works so much better as a delusional heel right now (he actually draws heel heat after his heel turn, a-ma-zing), Brock will have to turn face. Address the crowd cheering him wildly.
maybe Paul Heyman - Kinda pains me... actually really really pains me, but I feel that in a Brock - Punk feud, Heyman would work better as the manager of Brock instead of managing Punk. In the angle that Brock is in right now (sociopathic machine, only barely controllable by Paul Heyman) they cannot afford to turn Brock just like that, and so I fear Heyman will have to go with him for at least a short while. ...oh god, heel Heyman is just too good, disregard all of that.
Cody Rhodes - Have him shave that godawful moustache off and turn him face already - he's better than jobbing to Cena and other higher tiered faces, i'd even go as far as saying he is a possible main eventer now that he has a singles career in front of him. If I remember correctly, Goldust was a heel last time he was active in WWE, so it just comes naturally to have him feud with his brother as a face.
Antonio Cesaro - The crowd already has respect for him, if you remember him neutralizing The Great Khali and getting quite a few cheers for that. With his charisma and speaking ability, all that's really left is eliminating that "I hate Americans" side of his character and he makes a natural face. That respect would turn into affection pretty damn quickly.
Tensai - Well, I think for the moment he should turn face to team up with Brodus Clay. After a few month of this dancing tag team (you could just have them as a comedy tag team) mostly losing all their matches they could snap and both turn heel, to pair up as a team of monster heels. To be honest i'd rather see that than Brodus Clay turning all of a sudden.
Jack Swagger - Sure, why not? I don't get why he didn't return as a face in the first place, but it is not yet too late. He loves America, isn't that enough of a reason to be a face? He's a kind of generic heel and could truly shine as a face, time would tell. Personally I think it'd be pretty cool to see him team up with a face Antonio Cesaro. The All-American American and the 'converted' guy who embraces America now.
- Heel Turns -
The Miz - Does ANYBODY think it was a good idea to turn him face? Do whatever you need to turn him back, have him assault Ric Flair for all I care (remembering Ric Flair passed on the Figure-Four) blaming him for his losses against Cesaro. When you turn Cesaro face, turning Miz heel again just comes naturally. His character didn't even CHANGE upon his turn, and yet now everybody is supposed to cheer him even though he is still as annoying and heel-esque than before.
Kane - Well, one of Team Hell No should turn, and I think in what is likely going to be one of his latest runs Kane should be a heel once again before being inducted into the Hall of Fame, showing what he's truly made of. Daniel Bryan is way too over with the crowd to be a good heel and he does not have the charisma to change that around completely (yet), and so that leaves Kane as a new monster heel, a role that fits him much better anyway. He can beat up Zack Ryder some more.
Randy Orton - Not really too much to explain. The Viper feels much more comfortable as a heel. To really turn all those fans of his effectively though, he will seriously have to step on some toes. At, shortly before, or right after EC is a perfect opportunity for assaulting some seriously over faces... he could prevent someone from participating by giving him a beatdown before EC, he could let his frustration out at someone like Rey Mysterio in case he does not win... lots of different potential angles.
Sin Cara - "HBKistheHOF" kinda brought the idea up for me. I don't think they will turn Rey Mysterio, who has been a face and a role model for the kids for so damn long, into a heel shortly before his retirement (look at him, it can't take long), so that leaves Sin Cara with a heel turn. Besides, there aren't really any heels that can pull this high flying moveset off, and Sin Cara could complain about always standing in Rey's shadow and that he does not need Rey and blah.
Zack Ryder - Eh, I do not _really_ like the guy, but if he wants to actually wrestle again, he needs to become heel one way or the other. Have him go snap at the fans over the internet for not supporting him properly and not enforcing that they want to see him on TV. He got big on the internet, now he can turn heel over the internet as well. It's heel or bye.
Triple H - As a company guy, heel types work much much better than face types. You could somehow incorporate that "booking himself to win matches" angle that he has been given so much heat for by the IWC, and I believe HHH has the mic skills to not just seem like the second reincarnation of Vince when he does turn heel.
Honorary Mentions
Dolph Ziggler - Lots and lots of people want that on the internet, but I think it wouldn't work out that way, it'd flop like the face turn from The Miz - let him cash in first and have a semi-successful run as a heel before he turns, so he actually gets a reaction when he does and doesn't have everyone not on the internet go "Meh".
The Shield - I think they should stay as a heel stable and really establish themselves as that some more before they split and let Seth Rollins turn face. They have barely been incorporated in storylines, all they have been doing is randomly assaulting people. Have them be like Nexus for a while, only better and not buried by John Cena alone.
John Cena - Won't happen, and can't happen. The way the company is built right now does not allow for their face to become heel.
Chris Jericho - Think he should stay face for at least a while - have him feud with Ziggler, why not, and then when their feud is over, it could end in a double turn for the two of them, with Jericho then being able to feud with Ryback or Sheamus as an actual legitimate threat (if he's still working in the WWE then).