ExtJs-SeamRemotingJsonStore is a project mainly written in JavaScript, it's free.
Simple integration solution for ExtJs clients and Seam backends
This solution was created when I needed some glue for a proof of concept I was doing back in 2008. It was originally developed for ExtJs 2.x but the current version should work with 3.x.
For an in-depth discussion on this code and the assumptions it puts on your Seam components please read the following:
Integrating ExtJS with Seam: The SeamRemotingJsonStore
Integrating ExtJS with Seam: Error Handling
Integrating ExtJS with Seam: Client-side Form Handling
Integrating ExtJS with Seam: Server-side Request Processing