I've just released a plugin for WordPress that allows a WordPress based site to run a simple web based petition with e-mail confirmation of signatures.
It's very much a testing release. The software works for me but may not do things that other people might expect whilst running a simple petition. The plugin is available from:
http://www.freecharity.org.uk/wordpress-petition-plugin/
I've developed the plugin with WordPress 2.3 but I don't expect any problems with the 2.2 branch. It's my first publicly released WordPress plugin so if you'd like to give it a go and send me some feedback I'd be very grateful.
Regards,
James