You can find a monitoring tool to check: page ranks # of referring sites position in SERPs for search terms analysis of main back links keyword density supports both Google and Yahoo historical graphs Here is one sample: and here is another one: Please review!
it is a usefull tool, maybe you can put a option to select the main referrers by PR, or to show them by PR. The number of referrers on Yahoo how is obtain, if is the same number as number of links the tool is wrong.
I will show the main referrers by PR. This is one of the features that I plan to implement soon. As for the number of referrers by Yahoo. This is a little different than the number of back links to the domain. The idea is that the same referring site might have many back links to your domain and in this view they will be counted as one (only one referring site).