I've made a simple link co-op for photographers and wedding-related businesses. You add your URL and info, upload the link file to your website, and other websites link to you. No websites link directly to each other so the link juice isn't diluted. It isn't pretty, and it isn't without it's potential flaws, but from what I've seen it seems to work very well. That being said, use at your own risk. http://www.papertigermedia.ca/infinitelink.html