There are a many sites that offer free link popularity checks for your URL. Why is it so important to have sites that link into you? Google and other search engines appear to be placing more value on links that are coming into a site, than they used too. It used to be that optimizing keywords and enhancing your meta tags would help. While the keywords and their placement is still critical I have seen articles that meta tags may not hold that much weight. Remember though that you want to be linked too quality sites, so if you are linking to sites that have been blacklisted by Google and other search engines, you will only hurt your chances of getting ranked higher in search engines for your keywords and topics.