As far as paitings go, my favorite is Stary Night from Vincent Van Gogh. Other paintings of his such as Irises and Cafe Terrace at Night are also really good. I enjoy several works from Thomas Kinkade, too. Best of luck to you!
Hard to pick just one. But here's one of my favorite paintings:
"Wheat Field With Cypresses" by van Gogh.
For more modern pieces, I like this sculpture, "Expansion" in NYC: