Question:   "I want to put an email responder form on some of my websites,  what do you recommend?"

Answer:  The best I've found is Form Processor Pro.  It does everything:

     - Multi-page forms
     - Error validation
     - In form computations
     - Thank you/confirmation page
     - Thank you/confirmation E-mail auto responder
     - E-mail form content to one or more recipients
     - Store form content in a database

I've used it on a number of sites.  You'll notice how the form
itself, error page, thank you/confirmation page, and thank
you/confirmation E-mail can be styled as you like to match
your site.  Here are a couple of links were I've used it on that
you can try (make a required field or misformatted E-mail
address error) to see how it works/looks: 
 
     http://ctua.org/page_fs.htm (better example)
     http://www.epstar.com/ep_dn_ta.htm (shorter)
 
Here's a link to the product overview:

     http://www.email-form.com/overview.html

I already own a server license for the Perl version so you
don't have to buy it (let me know what domain(s) you want it
on and I'll set it up).

Here's a link to the complete online manual:     http://www.email-form.com/online-manual/index.html