Othman Ouahbi has a very nice example on his blog on creating automatic updating select-boxes with Ajax. If you change the first select-box, it updates the next selectbox accordingly.
Ahsanul Bari created a nice list of links to articles on the use of Ajax in CakePHP. Some of the parts covered are: Getting Started AutoComplete Ajax Redirect Ajax Validation Encoding Ajax Uploader So head over to Ahsan’s Laboratory and distover how to implement some nice ajax stuff in your web-app!