My 12th-grade calculus and physics teacher really impressed me, in part because he was the first adult who really treated me like an adult. I also remember appreciating the fact that, on the first day of class he went around and talked to each student individually and asked us if we were working, and how many hours. I was the only kid in that peer group that consistently worked a lot, and it was nice to have him recognize that.
Another teacher that really impressed me was my high school band teacher, who really liked what he was doing. I'm Facebook friends with him today 30 years later, and he's proof that you can enjoy your work for an entire career.
And finally, my second-grade teacher was a cute young redhead that I liked more than a seven year-old should. I actually sent her an e-mail a couple of years ago, not to confess my crush but just to say hi and let her know that I enjoyed being her student. She sent a nice letter back and included photographs that she had taken in her classroom that year that included me. It turned out that it had only been her second year of teaching, so she remembered it well.