Alcohol, as has been well documented.
Weed, occasionally during my early 20s. I had a friend who was fairly into it, and I would inhale when I went to her place. I haven't used it since I moved away from Edmonton, except for once a couple of years ago when I met up with her again. We shared a joint for old times sake. It was ...interesting, and fun at the time, but something I can do without. Also, due to my asthma, smoking anything is pretty unpleasant for me. Maybe after legalization they'll have some THC gummy-bears or something that I could try.
-k