Depends on what kind of mood. "I gotta feeling" by Black Eye Pea is pretty good for getting psyched before heading out with friends to go drinking/watch a movie/play games.
"You're the best around" (from Karate Kids soundtrack) is my go to song when I need to lift my spirits. I played the song before the start of every exam (not kidding).
Finally, "Highway to the Danger Zone" by Kenny Loggins (Top Gun Soundtrack) and "Life is a Highway" - Rascal Flatts version (don't knock it, it's a good cover) are both good songs in my car mix repertoire along with "Bounce" by Timbaland.