OpenRefine (formerly Google Refine) is a powerful tool for working with messy data: cleaning it; transforming it from one format into another; and extending it with web services and external data.
Using OpenRefine, by Ruben Verborgh and Max De Wilde, offers a great introduction to OpenRefine.
Another introduction in German is Datentransformation mit OpenRefine, part of a seminar for librarians.
Visit the official web site for videos and full documentation.
• Recommended by: Oleg Lavrovsky