Personally, I like a font that puts a slash of some sort through the zeros. Without that, the zero and uppercase O seem too close to me, too easy to mistake. You also need fonts with a serif, as that really helps to distinguish betweel a lower case l, the number 1, and an upper case I, even lower case i.
Monaco is my choice. And monospaced is really important for coding. Never program in a proportionally spaced font.