The following web sites offer excellent guidelines for grant proposal writing. Some include advice on letters of inquiry and sample proposals as well.
Grant writing handbook for nurses (2009) -SL Bar WY 20.5 H758g 2009
Write an effective funding application : a guide for researchers and scholars (2009)- Langson HG177 .W35 2009
The complete writing guide to NIH behavioral science grants (2008)- SL Reference WM 20 C736 2008