I was involved with a project a few years back that sought to match angel investors with young start-up companies. It was an interesting and enjoyable experience. Part of that process involved helping companies with thier executive summaries and business plans. Here is a good blog from Guy Kawasaki (www.garage.com) that covers the finer points of executive summary writing.

http://blog.guykawasaki.com/2006/04/the_art_of_the_.html

http://www.garage.com/files/Writing_Execsum.pdf