This plugin does what the iContact Widget cannot do:
It submits the form, and returns the success/fail message, via AJAX without redirecting the user to any other page than the one you're on.
This is obviously ideal if you want the form to appear and submit in a lightbox overlay, for example. It's amazing, I tried for three days to hack other widgets to do this, and I could not figure it out.
Author says this plugin is "beta", which only means he's a perfectionist. This is the best written iContact plugin out there, in my opinion. I wish i just tried it out before hacking for the last three days.