aFormMail
Absolutely free, I'm using it on one of my sites to collect mails. It works as follows:
If a surfer wants to download a file, he has to enter his name and email on a web form, and then gets an autoresponce with the download link.
You get the emails, IPs, time stamp, etc emailed to your email. The script is suppose to collect all the emails in one file, but I couldn't make that feature work. Yet again I'm not very clued about scripts, and I didn't really worry much about it.