The MIT Educational Studies Program, where I taught many, many classes, directed some programs, and ran the organization for about a year and a half.
Canada/USA Mathcamp, where I've taught a few classes on-and-off in-between the many other counseling duties I had there. I've archived problem sets from Mathcamp classes I've taught.
The Boston Math Circle, where I taught for one semester (spring '04) and also gave two guest lectures.
The MIT Experimental Studies Group, where I taught 6.001, the introductory computer science course at MIT, for two semesters.
The UIUC math department, where I'm TA'd Calculus for Business.