There are a few simple rules I have for code fonts: 1.) Monospace - I don't really go nuts about aligning things, but it is nice for looking at multi-line strings in code. 2.) Characters need to be distinct. l (lower-case ell), i (lower-case eye), I (upper-case eye) and 1 (one) cannot appear identical. 0, o and O shouldn't be the same - bonus if zero has a dot or line through the center.

Visual Studio defaults to Consolas, which is nice.