We embedded a form on our wedding website, but if I were going to do it again, I would use my friend Kevin's company, Wufoo. I'm getting ready to use Wufoo for another project I'm working on right now, and I adore it.
Specifically, I love how witty and personal the interface is. After I signed up, I received a message that started with "A Glorious Welcome!" When I log in to create a form, it says, "Holy tabula rasa! You don't have any forms! Let's go make one!" And the tagline under "Form Manager" says, "O, what men dare do!"
It cracks me up.