Guide for Proposal Writing
This guide from the National Science Foundation provides insight into the proposal review process at NSF as well as information about preparing a proposal using NSF-specific directions. The section called Advice to Proposal Writers contains information of a more general nature, including tips to make proposals more competitive. Note that this guide was written by the Directorate of Education, so the Intellectual Merit information is education-oriented rather than technology/science-focused.

EPA Tips on Writing a Grant Proposal
The Environmental Protection Agency (EPA) offers some excellent general information on writing a grant proposal and submitting to EPA.

Grant Writing Tips Sheets
The National Institutes of Health provides numerous resources to assist grant proposal writers. This web page provides links to many of those resources. General resources include an explanation of the NIH Funding Mechanisms and descriptions of the review process. In addition, many of the individual Institutes provide tips for applying the their Institute for funding.

The Art of Writing Proposals: Some Candid Suggestions for Applicants to Social Science Research Council Competitions
The Social Science Research Council has produced a succinct guide to writing a successful proposal. While the examples are from the Social Sciences, the information is generalizable.

A Proposal Writing Short Course
This proposal-writing guide is available from the Foundation Center Web Pages. It is short but covers the basic parts of a proposal for foundation funding, including what information to include and tips for what to avoid. In addition, there is a useful section describing Letter Proposals.

Guide for Writing a Funding Proposal
Several institutions of higher education offer useful guides to proposal writing. This particular site, authored by S. Joseph Levine at Michigan State University, has an interesting presentation of proposal sections, each of which is followed by writing tips and proposal examples to illustrate various points. A particular virtue is that the author is open to suggestions for additions and/or corrections and he updates the Guide several times a year.

Grant Writing for Success
This excellent PDF is a Grantsmanship 101 class written within the context of NIH, NIMH, and NIDA. It also includes a good presentation of the member institute websites and a short presentation on the Computer Retrieval of Information on Scientific Projects (CRISP) system.

NSF (National Science Foundation)

NIH (National Institutes of Health)

Social Sciences

Humanities

Arts

USDA (United States Department of Agriculture)

Foundations