Currently (Fall 2009), I am TA'ing 21-127 Concepts of Mathematics, lectured by Prof. John Mackey (course webpage). My office is Wean Hall 6207; I'll be there for regular office hours each Tuesday 10:30–11:30 and Thursday 4:00–6:00, but if you can't make those times (or have any other questions), just drop me an email (preferably with "21-127" in the subject line), and I'll be happy to work something out.
Spring 2007 21-121: Integration and Differential Equations
Summer I 2009 21-120: Differential and Integral Calculus