Wufoo is an online custom form creation application that enables the creation of quick and easy online forms. The interface is extremely intuitive and smooth to use. Wufoo is still under development but you can visit the site and play with the public demo. Also check out the screen-shot from one of the forms I set up recently.
I am not sure quite yet how Wufoo forms will be integrated into your own site so I will be interested to find out more how Wufoo plans on easing implementation. I am sure more details will be offered up by Wufoo as its launch date draws closer.