Okay, so if you've seen Winter Soldier, you know that Arnim Zola's contribution to the plot device was an advanced algorithm that lets Hydra predict someone's future behavior based on their past actions. Between this and the "The Clairvoyant is someone with SHIELD clearance!" revelation of last week's Agents of SHIELD episode, it's a pretty obvious setup for Zola to be the Clairvoyant.
However, there's plenty of objections to that. Here's a few of the big ones:
1) Why would Zola be puttering around setting up his own organization when he's part of Hydra already, and Hydra is getting ready to run SHIELD and conquer the world?
2) Zola's kinda dead anyway. He was backed up on tape, and his bunker was blown up. Pierce even mentioned that Hydra had lost Zola as the price of trying to take out Cap.
3) Making it Zola would basically steal the thunder from SHIELD's driving plot, since it would have been resolved almost as an afterthought in Winter Soldier. Plus, making it someone who wasn't even a suspect in the show is kinda dirty pool. At least make it Agent Hand, or Agent Garrett, running their own side game.
All valid concerns. But I still think Zola's a very good candidate, and here's how I think it will play out.
Arnim Zola used the algorithm to predict the chances of success for Hydra, and not only didn't much like the outcome, he also figured his demise was almost guaranteed to be a part of it. To wit, the only reason Hydra never moved him out of Camp Lehigh was that they clearly wanted to be able to erase him once he became inconvenient. Of course, he was no use completely isolated, so he found ways to back himself up to an outside system, and started working his own game. If Hydra ever decided to forcibly retire him, he'd have a new position waiting for him, as head of his own splinter faction.
Deathlok isn't just a useful asset, he's a testbed for technology intended to give Zola a body again. Hand or Garrett (or Triplett, or whichever cast member is the mole) isn't merely a Hydra agent, they're Zola's insider, who has been told the Insight project was likely to fail and is angling for a position in whatever shakes out. So, just as Strucker has been running his own game with Loki's staff and the not-Mutants, Zola has been preparing the groundwork for an independent group with him as the leader.
Oh, and as an added bonus, the actor who plays Arnim Zola isn't exactly an A-lister. They could easily afford to have him as a series regular once his identity is revealed. [Later note: It has been pointed out to me that Toby Jones is a bit closer to the A-list than I thought, so having him in person would probably be too expensive. But a few voiceover bits, and then give him a new actor to go with his robot body....]