Yahoo decided to shut down Yahoo Site Explorer, the best tool to see the backlinks to your site. Since Yahoo now works with Bing they merged Site Explorer into Bing Webmaster Tools. So, now what? You can go and use Bing Webmaster Tools , meaning you have to sign in and check the backlinks to your verified sites only. Also, the number of backlinks is lower than Yahoo Site Explorer. Finally you can’t check the backlinks to other sites, for example a competitor.
All you can do, is search on Google for a similar tool, but there are not many options. You see, most of these tools used Site Explorer to gather links.
The best tools I found are:
http://www.backlinkwatch.com – Right now this is the best alternative
http://www.opensiteexplorer.org – Another good alternative
http://www.majesticseo.com – This is a paid tool. It has a free version but shows only 5 backlinks.