Hi Sam,
Are you the merchant or the marketer?
There are a lot of software (both free and paid) out in the market, all for various purposes.
For complete marketing solution, I would recommend
Web Automation Center. You can get email autoresponder, affiliate program manager, mailing list manager, rss autoresponder, ad tracker, membership manager, support center manager all with one price. A great tool for both the merchant and marketer.
Damien