Every web site that participates in your Banner Exchange has your message on it. This one is a no brainer. You just approach other similar ezine publishers and ask if they would like to swap ads with you. This dramatically improves your exposure to the market. Try to limit the amount of advertising that you place in your ezines so that you don't overload your readers.
Some publishers send out special ad sheets that are separate from their regular newsletter.
It's also a good idea to key code your ads so that you know where the responses are coming from. This one isn't for everyone. But, if you have an ability to write interesting articles that would appeal to a broad base of readers, you can generate a lot of traffic for free and possibly even get paid for it. You don't have to write about marketing or the Internet. Just find a subject that you are knowledgeable in and start writing.