This is my current favorite. It's by Edvard Munch. It is called Starry Night. I like the colors in the painting (it looks a lot more purple than this at the Getty). There are a lot of cool aspects to it, but my favorite part is the shadow that is cast on the fence. It is supposed to be the shadow of two lovers holding each other.
Art I Like A Lot
This one is by Salvador Dali. It is called "The Rose."  I like the landscape underneath almost as much as the rose itself. I think the two parts of the painting contrast each other really well, making the landscape even more barren and the sky and the rose more vibrant. 
Magritte is one of my favorites just because his paintings are not that difficult to figure out once you look at his titles. He's also not quite as grotesque as Dali. Seems like his stuff is more fanciful than, well, psychotic. This one is REALLY interesting to me. Has been catching my eye ever since I first looked at it.