There are a number of websites with free tools for a linkpopularity check such as linkpopularity.com and marketleap.com. You can type in your partners URL and check through the list of links in each search engine to see if they are linked to you.
This could take quite some time depending on the amount of link partners you have. You could also go to Google and type in the search box link:www.yoursite.com or "www.yoursite.com" to see who is linked with you. The first method will only show you the page that your link is on if it has a PR4 or above.