ASP.NET AJAX v1.0
I'm sure your all aware, but if not, Microsoft have released v1.0 of the ASP.NET AJAX, previously know as Atlas. They had planned to release it as part of Orcas but it was deemed to groovy.
On a related subject I tried out the I.E. Developers Toolbar Beta today, it was a quick look, and although it's still Beta it's worth the download.