There are a few ways to become involved in a link or banner exchange.

One way is to email moderators of sites that are related to your wiki and request a swap. Many fan-operated sites will have Admin who are more than willing to exchange links or banners with you, provided you are running a legitimate site on a similar topic.

List your site information and banner on the Dry Paint Ads wiki -- A site designed specifically for advertising wiki's hosted by Wetpaint.com.

A variation on the link/banner exchange is joining a Web ring, where you will be linked to many similar sites. However, not all links are created equal. You will rank higher on search engines if you are linked from sites that are high-ranked themselves. Download a free Google toolbar from SEO Tools that can help you determine how each site you are visiting isranked ranked.(on a scale from one to ten).