I came across this cool tool a few days ago called TouchGraph. Simply type in your domain name or the keyword you are targeting, and let it do its magic. This tool uses the Google “related sites” query and displays a very cool chart. I tested a few out so far and find that they will display a lot of related sites and competitors. This means that you can go visit these sites, and ask the webmaster if you could write and article for them. Its easy to tell who runs the market for the keywords you input by the size of their circle.