A few years back I realized that I had trouble diferentiating between the movies I liked and the movies I loved from the early part of the year. Roger Ebert has always suggested that this was true of the Academy and why the Oscars have such "short attention span." He recommended a midyear ballot to go along with the end-of-the-year ballot combining both to create the nominations list.
For me, I decided a top 5 usually works. I wait until July 15, since the first few weeks of January are generally a wash for new releases, and so 7/15 is a little closer to the mid-point. This year has had a number of promising films after a pretty lame first few months.
I have eleven "nominees" for my top 5 this year— four at the top: Fanboys; The Hurt Locker; I Love You, Man; and Up— plus, Adventureland, Coraline, The Hangover, Monsters Vs. Aliens, Moon, Star Trek, and Sunshine Cleaning.
My top 5 2009 so far (listed alphabetically):
The Hurt Locker
I Love You, Man