There haven't been too many outstanding MAIN themes in the past few years that I've liked. Recent soundtracks I like mostly excel because of their nice secondary themes and how they're cleverly weaved throughout their respective scores.
I guess I'm growing fond of James Horner's new main theme for Spider-Man, though. It's wonderfully developed throughout ASM's score as it starts off more mysterious and pretty understated, having bits and pieces of it only hinted at during the first half of the soundtrack. Then, once the action material starts and we get to the climax of the film, the theme flourishes into its more memorable, heroic, and soaring variation.
If they manage to keep Horner for the film's sequel, I'll really look forward to how the theme will be handled then.