National Science Foundation
Dear Colleague letter (2008) -- explanation and examples of broader impacts proposal requirements
Grant Proposal Guide (GPG) -- detailed instructions for preparing a standard NSF grant proposal
"A Guide for Proposal Writing"
Online Evaluation Resource Library (OERL) -- evaluation plans, instruments and reports that may be valuable in defining a project and proposal evaluation plan
Grants.gov applicant resources, including FAQs, user guides, and animated tutorials
Toolkits (Texas A&M Office of Proposal Development)
US Department of Agriculture
US Department of Education
"The Art of Grantsmanship" - Jacob Kraicer
"The Art of Writing Proposals: Some Candid Suggestions for Applicants. . ." -- from the Social Science Research Council, but the advice is equally applicable to all proposals
"Murder Most Foul: How Not to Kill a Grant Application"