Prototype looks good too, but I haven't explored it too much.
I think that for my use XML and XSL will stay on the server, and the client side will only use JSON.
Good article on XML, HTML, and JSON:
There are some nice json libraries:
E4X looks interesting too, but of course Microsoft lacks support for this standard:
I'm having a blast with jQuery. I just added tablesorter to PBooks and 1. it was easy and 2. it works really well. I then found this:
which might be the right solution for me. I've been wavering between XML and JSON for updating content, and I think this might clinch the deal for XSL. I don't think I'll be doing many heavy AJAX data downloads, instead downloading all the data in one fell swoop and then perusing it with a method like the tablesorter pager.