Are there any good LaTeX templates or classes available which comply to NSF formatting requirements? In particular, I'm looking for a template for the "biographical sketch."
Here you can find a LaTeX template customized for the NSF-style 2-page biographical sketch:
Maybe you can customize that template for your needs.
Since the guidelines for NSF grant proposals are quite minimal, no one seems to have created a specific LaTeX class file or package for them. The thing that comes closest is the following page from the Math department at MIT: Grant Proposals.
But these files are really just basic templates for what should be in the document; they don't do much formatting in the way that a properly created class file would do.
For the biographical sketch, it might work to use one of the CV packages to do this. See this question for some ideas on that: LaTeX template for resume/curriculum vitae