Max Kiesler has created a list of 30 Ajax Tutorials covering various common usages.
Tutorials cover:
Ajax Client-Server Communication
Ajax Drag and Drop
Ajax Forms
Ajax File Uploader
Ajax Framework and Toolkit
Ajax Getting Started
Ajax Image Gallery
Ajax Keyword Suggest
Ajax Live Search
Ajax Sorting
Ajax Tabbed Pages
Although not all of these actually use Ajax (only javascript) – they are still worth a look at. Ajax is a bit of a buzz word these days – so you’ll find many new JavaScript tutorials are masked as being Ajax (which is asynchronous, where many will be strictly client-side). There are great benifits with Ajax, but many things can be done without it!