Oh, good grief!
Another impossible poll!
George's solo work is so varied, this list would have to be 20 choices long, and I still don't think you'd come close to picking everyone's favorites.
I'm going to be really rigorous and just pick:
ATMP 1: What Is Life and Let It Down
ATMP 2: Beware of Darkness and Hear Me Lord
Brainwashed: Pisces Fish and... and... the whole rest of the album!
Seriously, on both these albums, there's not a song I would skip (except the remake of MSL but that doesn't really count).
But as for songs that just come out of the blue, "Cheer Down". I still remember hearing that in the theatre and sitting bolt upright and saying "George!" (I think I even said it out loud.) :B Great song, and always makes me feel happy.