I came across a couple of free form builders on digg.com The two were Wufoo and FormAssembly.
These both are web-based tools which allow you to build really good forms. You can build varied forms and do authentication on them based on their properties (alphanumeric, password etc)
Both tools are in their beta but are worth the mention. Wufoo has a demo which allows you do see what you do with it. You can’t however download or do anything else with it.
A seemingly better tool would be FormAssembly. Better to use interface, more options and you can download the form source along with the CSS to use on your website. You can even host the form on their website and manage responses. They have Form templates, so if you need to setup a survey, an invite – easily done. Also available is a bunch of CSS styles to fix your form.
I’m going to look at the latter to learn some JS to authenticate forms. About time I learn it with AJAX and stuff going around.