ChronoEngine's ChronoForms is a vastly superior form handling solution, and I strongly recommend it over the other entries in this field. Nothing else comes close for flexibility, ease of use, and back-end organization.
Yes, it's "commercial". But the paltry $25 fee allows up to five domain installs, and is a preposterously low price given the power it puts at your fingertips.
Major mega-kudos to a commercial 3PD who has made this incredible Enterprise-class extension available at a consumer/small-business price! This is the example that all commercial 3PDs should follow.