
Every Search Engine expert knows the importance of backlinks.It is not only important to get as many quality back links for a website owner as possible but also know the sources where your competitor website has gathered backlinks from.The revealed source of strength of the opponent website helps seo's around the world focus on strategies for grab their websites pie as position in Google.
There are couple of sources below to find the number of backlinks and their PR your competitor enjoys.
Checkbacklink.com
The website is fast to produce result and the accuracy is somewhat OK.However , the page rank also is produces wrong PR for some high ranking websites.
Check it here - http://www.checkbacklink.com/

Backlinkwatch.com
The most popular among seo analysts and newbies.The results are i believe 70-80% correct.The graphical interface is messy so casts a wrong impression but a definately useful free seo tool .
Check it here - http://www.backlinkwatch.com/
Alexa.Com
Alexa apart from providing details about websites also gives you an option "Sites Linking In" - this is where you get a cue what types are sites are boosting your competitor's search rankings.
The drawback with alexa is that they fail to provide backlinking data for newer and not-so-immensely popular websites.
Google Webmaster Tools
Google webmaster tools is a free website service by google for webmaster to help them tweak and enhance their websites performance in google.Its has an option in left pane called
Your site on the web--->Links to your site where all incoming links to a website's owner's are displayed.It is for checking self site links accurately.
Check it here - http://www.google.com/webmasters/tools/
Yahoo Engines
Yahoo also helps you find backlinks towards a website.Not all links are shown but provides a handsome of information and cues on which you can build your seo plans.
In the yahoo's search box type this pattern link:http://www.<competitor's domain>.com (if its a .com , else , .in,.au or anything else)
Check it here - http://search.yahoo.com
You can also share your findings with the help of comment box below --
Bye !
HSJ