A page on the Distributed Proofreaders project advises people who are trying to find typos in scanned and OCR'ed texts to try DPCustomMono, a font specifically designed to make it easy to catch common OCR errors. Distributed Proofreaders are volunteers who check out a page or more of scanned text from the Project Gutenberg archives and check it for typos, improving the quality of the text. DPCustomMono's characters are designed to maximize the difference between ones, lower-case ells, and upper-case eyes, as well as other lookalike glyphs.
(via Making Light)