Free Ninja Tips
Both Underground Ninja Secrets and The Official Black Dragon Ryu - Ninjitsu Training Manual offer free ninja training tips.
If you go to The Official Black Dragon Ryu - Ninjitsu Training Manual you'll see a link on the left hand side of the page (about half way down) titled - 'The Five Lessons Of Ninjitsu', follow this link to get 5 days worth of great FREE Ninjitsu lessons!
The Underground Ninjitsu Secrets also give away free ninja tips. If you visit their site and sign up to learn more, they will send you an e-mail with a link in it to a Special Report (unadvertised!) which teaches you some really powerful stuff.