Excellent Basic AJAX Examples
ClearNova has probably the best single page of AJAX examples available with downloadable source.
The downloadable samples include full JavaScript & Java Source, a sample database for any SQL database, and a PowerPoint presentation.Source : ClearNova : Basic AJAX Examples
Examples include:
Ping!
Track Changes
Drop Downs & Form Handling
Get Customers By State (Parse Plain Text)
Get Customers By State (Parses XML)
Google Suggest Hack
Activity Log