1. Give visitors a free subscription to your e-zine. Almost everyone is publishing a e-zine nowadays so it's important to give something extra with the free subscription. You could offer a free gift or advertising when people subscribe.
2. Provide your visitors with free content. Your content will be more magnetic to your visitors if it's up-to-date or original. You could also offer people the option to republish the content in their e-zine or web site.
3. Offer a free online directory. The directory could be full of interesting ebooks, e-zines, web sites etc. If people find your directory to be a valuable resource they'll visit it again and again.
4. Give your visitors free ebooks. You could also include your own ad in the ebook and permit others to give it away. If you don't want to take the time to write one, you could ask other writers permission to use their articles.