What would be the quickest opensource way to have an searchable index of documents? (pdf, doc(x), et al)

Although my organization primarily uses Google Docs and I would suggest Google Search Appliance to an organization of reasonable size, what would be a good solution for a small business or government organization to index all their files and have them searchable?

The goal is to reduce redundancy and not have to rewrite certain documents and if possible reuse relative documents in order to prevent inventing the wheel twice.