Starting an email newsletter is cheap, easy, and incredibly effective. Regardless of what Internet business model you choose to go with, you should have your own email marketing newsletter.
Electronic newsletters are nice for this reason: Web sites are static; people find them, like them, and then all too often completely forget about them and never come back.
But if they sign up for your newsletter when they are at your site, you can go to them. I can't tell you how many times the above scenario has happened to me. I find a web site that I think is totally cool, surf around, sign up for their email newsletter while I'm there, and then completely forget about the site.
But then, within a few weeks or so, their newsletter comes and I'm like, oh yea! And I click through from the newsletter to check out their site again or take advantage of the special offers within the newsletter, etc.
If you decide to go with retail as a business model, having an electronic newsletter may be one of the most important things you do. Check out GreenFeet.com
See how they make a big push for you to sign up for their (very cool) newsletter? This is because they know that, most likely, you are going to visit their site and never come back again, unless you sign up for their newsletter.
Then they can actively engage you every month or so and reach you with special offers, cool features, or just updates on what's going on. It's not uncommon for retail sites to do 50% or more of their sales through email marketing.
It's also critical for content sites. As a matter of fact, there are some advertising based business models that are only a newsletter and make 100% of their ad sales that way. Once again, this is really nice for them because if they rely just on a web site people may or may not come back to visit, but if they sign up for their newsletter they will be in front of them in their inbox once a day, week, or month.
One of the content sites I help run generates a full 1/3 of its revenue from the email newsletter. That's quite a chunk.