The following sites provide useful information and grant writing tips. 

NIH Tips - Planning Your Application http://grants.nih.gov/grants/planning_application.htm

NIH Tips - Writing Your Application http://grants.nih.gov/grants/writing_application.htm

NIH Grant Writing Tip Sheets                                    http://grants.nih.gov/grants/grant_tips.htm

NSF Guide - How to Prepare Your Proposal                     http://www.nsf.gov/funding/preparing/