Tracking your backlinks is very important. Here are a couple methods to do so.
Sign up for google webmaster tools, it will show you a list of some of your backlinks. good article on finding your links from Google. http://googlewebmastercentral.blogspot.com/2007/02/discover-your-links.html
You can go to www.yahoo.com and put linkdomain:yoursite.com -domain:yoursite.com into the search bar.
I also recommend you sign up for Yahoo Site explorer and you can view a large portion of those who link back to you that yahoo has in its database.
http://siteexplorer.search.yahoo.com
type in the search bar site:www.website.com
Click the Inlinks button > click the first drop down and choose “except from this domain” then once that loads again move to the second drop down and choose “Entire Site”. This site has a few tools that are very beneficial. Get the SEO Link Analysis plug in by Yoast, it gives you on page analysis of the backlinks and is very useful. While your at it sign up for Yoast’sRSS feed. Sign up for our ProStores Tips and Tricks Feed as well.
There a lot of third party tools as well. http://www.seomoz.org/toolbox/backlinks is one i use a lot, it will also show you a historical list of your backlinks. It uses siteexplorer but like I mentioned before it will show you how many you used to have. So it provides a good basis for comparison.