This <A HREF="http://people.math.gatech.edu/~dmargalit7/tsr/grants.shtml">site</A> maintained by Dan Margalit has one example of a successful <A HREF="http://people.math.gatech.edu/~dmargalit7/tsr/career.pdf">NSF math proposal</A>, but in addition contains resources on how to write such a proposal (notably the sections on intellectual merit and broader impact) that might be even more useful than a specific proposal.