Wufoo is a fun, easy way to add forms to your website. It has its limitations, the most annoying of which is the maximum fields allowed in a form, but they are constantly adding functionality. You can create complex forms by applying rules to a form, and integrate your form with PayPal, Google Checkout, and Authorize.net in order to easily collect payment. I love it and have used it in several of the sites I manage. Wufoo plays well with other sites. It can be integrated with MailChimp, Campaign Monitor, and Freshbooks, to name a few.