OK here are my picks:

Williams and Maldonado and the possibility of them building on 2012 to become regular contenders.
The progress of Nico Hulkenberg, hopefully WINNING Sauber's first independent race. But podiums at least. I hope they don't lose ground by losing James Key.
Lewis winning a race for Mercedes
Toro Rosso returning to more like 2011 form because the drivers build on experience
The progress of Marussia with full windtunnel and Pat Symonds, and KERS!
Really hoping one of those bottom teams finally gets that point, but I think Caterham may slip back a little due to lack of funds. Marussia being over 4sec off the pace is too much to make up, so unlikely except in a crazy race.
And an even closer field overall.

Feel free to add what you are most looking forward to, people.