Hub Finder is a free tool for finding co-occurring backlinks to a set of (up to 10) urls. Each result will be a url of a page which contains at least two links to urls you input to the tool. They are ordered so that the urls which link to most of your input urls come first. So the results nearer to the top of the list are the ones which have the greatest 'hub-like' qualities. Hub sites are good sites to approach for links to your own site.However, don't just focus on the hubs near the top of the list, even though they may be easier to acquire. In fact, you may well find that the links that have the greatest impact on your rankings will come from sites with fewer out-going links, because the benefit can get diluted when a page contains multiple links.