The quickest way to do this is using the "Top Pages" report in Open Site Explorer.
Simply enter the root domain of the site you want to research, hit "search" then navigate to the Top Pages tab. This will show you the number of lining root domains to each internal page.
Here's a screenshot:
https://skitch.com/cyrusshepard/8baj7/open-site-explorer
+1 For Doug's answer. You can download the standard Inbound Link report from OSE. Make sure to filter for "external" links to "all links on the root domain" (or subdomain)
Open your report in a spreadsheet, The "Target URL" column will show all the URLs on the domain with an external link pointing to them. Here's another screenshot:
https://skitch.com/cyrusshepard/8bakm/microsoft-excel
Hope this helps. Best of luck with your SEO!
