This morning I pushed version 1.1 of my VZ Url fieldtype for Brandon Kelly’s FieldFrame extension up to GitHub. The code for this version completely rewritten to (hopefully!) eliminate some issues with ajax calls returning in the wrong order, leading to false negatives. While I was at it, I made the errors display in a pop-up box, allowing for more verbose errors without breaking the layout.
There is also one significant new feature. Previously, if the entered url was redirected to another site (i.e. http://google.com, which redirects to http://www.google.com) it would be displayed as an error. Now, a more helpful message is show, with the option to update to the new url.
Update: I have since updated VZ Url to version 2, which supports Expression Engine 1.6+ and 2.0+.