How to implement file upload progress bar on web?

I've tried various techniques and had most success with SWFUpload.

You create and interact with an SWFUpload object using Javascript, but uses a (hidden) Flash file for file selection, uploading and upload progress monitoring. You can specify a wide range of Javascript event handlers (uploadStarted, uploadProgress, uploadError etc.) that the Flash will call during the upload progress making it very flexible. It also implements a file queue, so it works well for single or multiple files.

Links:

• API documentation
• Demos
• Downloads

A good example of doing this without using Ajax is given at CodeProject by Nilesh Thakkar.