Painless Ajax for ASP.NET with Gaia Ajax Widgets
I found this library while researching the web for an alternative AJAX solution for ASP.NET sans Javascript. The thing is, if you know how to use those built in WebControls, then you already know how to use Gaia since most of its widgets mirror those found in ASP.NET. The window and autocompleter controls are very impressive.
Gaia makes the Ajax toolkit from Microsoft look ummm ... outdated. See for yourself here.