I like this one, thanks. It appears to be a lighter-looking (at least with my font smoothing settings) version of Courier (which is good because regular Courier is legible but quite heavy at small sizes). The "serifs" are actually slabs, just like in Courier.
http://www.ms-studio.com/FontSales/anonymouspro.html
edit: it sort of has serifs. kind of. well more than most sans fonts