There is a big push in the PhD program I'm headed into for candidates to apply for NSF grants (in fact, one of the required classes for the first year is a class on writing grant proposals, and as a final project, every candidate submits an NSF proposal). I'm assuming this is the same for any Science/Math PhD program, as funding is tight for many departments, and a grant basically makes you free for the University.
Are there any other options for Science PhD-level grants I could apply for?