Most of my current gaming is probably D&D 5E just because it's what guys in the store run and I can actually play instead of always being the DM.Really old school = OD&D, Metamorphosis Alpha, Boot Hill. A little EPT but it's a bit "out there" for me.
As an extension of OD&D, if I want a little more structure I like C&C and Amazing Adventures (very much the same, and hopefully Victorious soon) and DCC RPG for a particularly weird take on fantasy. C&C is so smooth to run.
Outside of the traditional, I enjoy Amber Diceless as being an excellent example of role playing with strange rules. I have an addiction to reading Ron Edwards' Sorcerer but haven't had much success playing it.
Other stuff I'm not sure how to classify: 7th Sea (roll and keep version), WEG Star Wars, funky dice Star Wars.