Ask HN: Backlink lookup tool for community discovery purposes?

Any free tools out there to perform backlink lookup for non-site-owners? i.e. given a page, show me a listing of pages that link to that page?

I'm thinking like a hackernews comments button, but generalized to the entire internet.

Reasoning:

I'd like a discovery tool that, given a blog post, reveals the community of other blog posts as responses. There are tools that show you comments given a page, but if I want to observe slow, considered discussion, blog posts are probably a better medium.

Feels like something google would be able to provide, given the basics of how pagerank is supposed to work. But searching around it seems this is only exposed through webmaster tools for the site owner, and even then I'm not sure it would give me quite the search functionality I seek.