You can use an AWeber extension for Joomla! that allows you to embed the AWeber opt-in form right into your site. This allows you to build your list and take advantage of AWebers autoresponders and delivery strength.

If you don't know about AWeber or why you should use it, then this is one of those "trust-me" things. For $19.00/month AWeber is the best email list service I've ever used. It's a critical component to building a long term business on the web.