I run one-shot games at conventions, mostly FATE and Dread. At the conventions I tend to join a lot of Mork Bork and Numenera games, although I've never GM'd them.
I also play in longer D&D campaigns with friends, but we've played other campaigns in Firefly (Cortex) and Star Trek Adventures.
FATE is my favorite for the flexibility. People tend to focus on making the story good as opposed to trying to work against the restraints of their character. Unfortunately most people in my friend group are Pathfinder/D&D focused, so we tend to go that direction.
Meanwhile I probably run No Thank You, Evil! the most lately, just because my household has become overrun with kids.
I recently received Triangle Agency, so I'm excited to try that.