Well you definitely need something to handle AJAX. I pick between Prototype and jQuery, depending on the project. Sometimes I mix and match with both, since jQuery can coexist.
Next, you need to decide whether you will transport XML/JSON and have client-side code stick in in the DOM, or eval the AJAX response. In the latter case, you need to be generating JavaScript on the server-side. I know the Ruby on Rails RJS piece of the stack can be extracted from Rails 3, but I'm unsure about Python, so you might be better off taking the former approach.
There's a lot you can do with regards to animation in Prototype/jQuery alone, but I like Scriptaculous, and I've heard good things about MooTools.
Making a GMail-like interface isn't all about XML-HTTP-Requests though. There's a lot of value in nailing the usability, the basic concept. Then there's maintaining the history, undoable actions, HTML fallback and such.
My best advice is to start building a decent static interface from the ground up, and when you have it nailed, just augment all the minor GET actions with AJAX first (like going back to the index after reading an email). Then enhance primary POST and UPDATE actions (replying, marking with a star, moving to archive).
Half way through, you'll probably notice most of the page reloads that remain are acceptable. At that point, focus on refining the original concept with new methodologies you picked up along the way.
It's just the way I do it though, make sure you investigate other suggestions to find a perfect fit (by the looks of it, GWT is quite a paradigm-shift).
Next, you need to decide whether you will transport XML/JSON and have client-side code stick in in the DOM, or eval the AJAX response. In the latter case, you need to be generating JavaScript on the server-side. I know the Ruby on Rails RJS piece of the stack can be extracted from Rails 3, but I'm unsure about Python, so you might be better off taking the former approach.
There's a lot you can do with regards to animation in Prototype/jQuery alone, but I like Scriptaculous, and I've heard good things about MooTools.
Making a GMail-like interface isn't all about XML-HTTP-Requests though. There's a lot of value in nailing the usability, the basic concept. Then there's maintaining the history, undoable actions, HTML fallback and such.
My best advice is to start building a decent static interface from the ground up, and when you have it nailed, just augment all the minor GET actions with AJAX first (like going back to the index after reading an email). Then enhance primary POST and UPDATE actions (replying, marking with a star, moving to archive).
Half way through, you'll probably notice most of the page reloads that remain are acceptable. At that point, focus on refining the original concept with new methodologies you picked up along the way.
It's just the way I do it though, make sure you investigate other suggestions to find a perfect fit (by the looks of it, GWT is quite a paradigm-shift).