Are you doing anything like what's in this video? Walking lunges, bunny hops are two of them. Besides some of the yoga positions, what do you do to enhance 1-leg balance?
One of my favorites is tree pose with moving arms - I bring them in and out, up and down with the breath, and to make it harder, then follow my fingertip height with my eyes - looking up at the ceiling and down at the floor. Once that is easy, I close my eyes and the final step is to add in as much of a backbend as I can pull off on one leg. (I think the next step will be with my heel raised...)
Other than yoga poses, I also do ballet and a bunch of moves on an Xerdisc while watching TV. (which is one of these - essentially a cheap and smaller version of a BOSU ball)
Sometimes I just stand one-legged, other times I do lunges or squats or whatever. It's very rarely a focused "workout", but I think when it comes to balance/1-legged balance, it's mainly a matter of repetition and practice, and the more you do the better.
I used to see it all the time when I was teaching yoga - I was teaching at a drug and alcohol rehab canter, and most of my students were very inactive and coming off of detoxing and had no balance at all. Especially some of the older ones had pretty major balance problems. I'd ask them to stand on one leg and get laughs because so many thought it completely impossible. So we'd start with a hand on a chair and the toe of the lifted leg still on the ground. But within a month, people who started there were generally in a real tree pose, balancing on one leg and moving their arms around comfortably. I think it's really remarkable how fast your body re-builds those neural pathways and your balance comes back. BUT, it isn't going to happen if you don't challenge it. And unless you're doing a yoga class with some focus on it or dance or something where it's a functional move... it's easy to forget to practice balance, I think.
I do credit my balance work for making my first day of skiing this season feel just like another day last year. Strength and fitness are great, but in a sport where we're literally sliding around, I think balance is a huge part of feeling comfortable.