Hmm tough, Clearks 2 is a good choice but I really enjoyed Talladega Nights, FFVII: Advent Children and X3
Little Man, Superman returns are the ones I liked most. Though there are few more to come and I am waiting for them
Not necessarily my favorite movie of the year, but I just saw The Prestige and it is very good and one you will talk about for a few days after. See it with a spouse or friend.
The Guardian was, IMO, way above average. I didn't see the big summer movies, so I'll vote The Guardian.