Whatever changes are going on in the search world, links remain the backbone of search engine ranking algorithms. You can have great design, put out amazing content and exclusive advice, but unless you're pulling the link juice you'll find it hard to rank well for anything competitive.

Backlink research is the cornerstone of every link building campaign. There are a number of reasons you might want to check backlinks to a site. When you just starting to optimize a website you need to check how many incoming links it has and what value they pass. Then you need to check the competing websites to evaluate the time and effort it will take to outrank them and decide whether it's feasible to target the search term in the first place. This is one of the SEO tasks that are just impossible to do by hand. Obviously you can't just visit random sites looking for a link. Luckily, there are a number of SEO tools out there that will help you check the linking profile of a website and shape your link building tactics.

1. Yahoo! Site Explorer

This is perhaps the most popular backlink checker out there. Yahoo! Site Explorer gives you the list of incoming links to the domain you specify. You can simply go to Yahoo! search and type in link:yoursite[dot]com and you'll be redirected to the site explorer where you'll be able to see who's linking to the site. The link: command also works on other search engines including Google, but they are known to only show a small random sample of a site's link profile. Yahoo on the other hand usually provides much more comprehensive results.

Site explorer is a great tool to run a quick backlink check on a site but it has a number of downsides. First of all it doesn't show more than 1,000 results per domain, so you'll need to weed out the internal links and check links to deeper pages to get more results. Second, it doesn't provide any info on whether the links are dofollow and pas on any SEO value, what anchor texts are used and other important data an SEO needs.

2. Backlink Watch

Backlink Watch is a free online tool that powered by Yahoo! site explorer. The results there are the same but you get additional info that's crucial for quality backlink analysis. Alongside with a list of links to a site you get to know whether the link is dofollow or nofollow, the exact anchor text of the link or the image for banner links and the total number of outbound links on the page.

3. SEO SpyGlass

SEO SpyGlass is a desktop application that queries a vast database of search engines to get a bigger list of links to a site. It's paid software with free edition available. The good thing about SEO SpyGlass is that it's able to provide a bigger list of links to a site (up to 50,000 depending on the site's linking profile) by using advanced search operators.

Together with the list of links the software also provides a wealth of information neatly broken down for analysis: whether the link is dofollow, Google PageRank of the linking domain and website, the number of the outbound links on the page, the SEO value of each link, whether the site is listed in DMOZ and/or Yahoo! Directory, whether the link is still in place or has been removed by the webmaster, the anchor text and much more.

4. Google Webmaster Tools

If you have a Google Webmaster Tools account you can check the incoming links to your own site that have been indexed by Google. To do this go to Dashboard -> 'Your site on the web' -> 'Links to your site'. There you'll get a list of sites linking to yours. In the Anchor Text tab you can see what anchor texts are used in the links to your site. This list doesn't include all the links Google knows about, still it's more comprehensive than the one you get if you simply use the link command on Google search.