Seeking module/technique for giving site visitors a download "gift" in exchage for their email
I would use Webform Rules Module. On submit and validation of an email address have a Rule that redirects the user to a download page. Of course, since it's Rules you might be able to conjure up all kinds of wonderful complicated things. I also found these lovely tutorials on Rules at NodeOne. However, you might be able to write a module faster than it would take to work through all those videos.