Luke W’s presentation on Best Practices for Web Form Design from the IA Summit 2007 and his followup post.
Icebrrg is another interesting form creation tool similar to Wufoo and FormAssembly’s FormBuilder.
CrazyEgg is Robbin’s new fav recommendation. Of course you can easily roll your own heatmaps. I like that CrazyEgg tracks clicks anywhere on the page (not just links) and that it supports HTTPS but it occassionally hangs up affects the load time of the page (even when you place it before the closing body tag). Another similar tool worth a peek is ClickTale. It records mouse movement, clicks and scrolling.