GrantProposal.com
Produced by professional grantwriter Elizabeth Brunner, this website outlines the steps of preparing a proposal and offers advice on researching funding opportunities, as well as providing sample proposals and letters of inquiry.  An excellent introduction to the principles of grantseeking.

CFDA’s Developing and Writing Grant Proposals
This article from the Catalog of Federal Domestic Assistance offers advice on preparing proposals for federal funders, including developing a project, gathering community or institutional support, and the various parts of the proposal itself.

The Art of Grantsmanship
Prepared by Dr. Jacob Kraicer of the University of Toronto, this is an excellent summary of advice for obtaining research funding.  It concisely covers designing a project, identifying a funding source, writing the proposal, and how the proposal will likely be reviewed.  A good brush-up before starting to write a proposal.