I’ve been meaning to volunteer with Project Gutenberg for a couple of years, but I finally signed up to help proofread scanned and OCR’d texts. The Distributed Proofreading project makes it very easy. Sign up, read over the proofreading guidelines document, and then you can view page scans and the OCR’d text side by side in their web browser tool and edit the text to make any necessary corrections. They manage to coordinate the proofreading of between 500 and 1500 pages a day. It’s a very easy process, and a single page isn’t too time consuming, so think about signing up yourself!