Component Art is good stuff
If you haven't seen the beta version of the new Component Art Web.UI Suite, check it out
I was already planning on using this stuff for the project I'm on right now, and with the addition of their new Grid control, now I'm thinking I might want to get it even for my own stuff. It's not cheap, true, but I think their new Grid control beats the snot out of the Infragistics stuff (in part because half of their site doesn't even work in Firefox). The Callback control, wrapping pretty much anything into an AJAX control is sweet.
These guys are really clever, and I look forward to seeing their source code too. Not a cheap subscription, but I think it will be worth it.