Create a free ebook and offer all who download the right to distribute it on their site or ezine. Encourage them to pass it on to maximize the free publicity. If you do not have ebook software, you can have an ebook created for free at:
http://www.ebooks-made-easy.com/

Once you have your ebook you can distribute it at software sites such as:
http://www.zdnet.com/downloads/ or
http://www.freewarehome.com

Quick tips on how to create, distribute and profit from eBooks are are at:
http://onlinebusinessbasics.com/articles/ebooktips.html

Don't forget the free ebook directories such as:
http://www.ebookdirectory.com