If I could get away with wearing yoga pants (yoga leggings) everywhere, I would. They feel like wearing no pants at all--no pants being the best kind of pants.
Unfortunately, I have a overly-developed sense of propriety and a half-baked sense of style, so I don't wear my yoga leggings in public except when actually going to/from yoga or when I'm sick (because to hell with everything when I'm sick; I'll wear what I want!).
Sooo... my answer is "jeans." Mostly. The skinny kind in a rainbow of colours. It's the closest I can get to leggings while still being vaguely appropriate. Also, I just gotta wear the hell out of that 'ish while I'm still young-ish. Once I'm older, I'm going to have to go all proper with trousers and the like, because I don't want to fall into the mutton dressed as lamb trap.