BASEMENT.ORG

Cool, this one has label tags, only doesn't use the for attribute to properly link them to their controls.
Getting closer though :/

There is a new online Form Builder called The Blue Form.
It features an AJAX style form builder but it also allows approval workflows to be assigned to forms. This means that once forms are filled-in, approvers receive an email asking them to approver or reject the form. Multiple approvers can be specified for the form and the form can be tracked through the workflow. Data can be exported from the system at any time.
This makes The Blue Form more of a process automation / BPM tool than just an AJAX form builder.

There's a more recent and detailed review of Wufoo, including a live data-entry form and several screen captures, plus links to other AJAXified formbuilders at http://oakleafblog.blogspot.com/2006/07/wufoo-challenges-infopath-for-form.html.