After purchasing Freebase the public graph database Google has also taken Freebases data mining application Gridbase under its wings. Now named Google Refine it still is a power tool for working with messy data, cleaning it up, transforming it from one format into another, extending and correcting it with web services, and linking it to databases like Freebase.
Version 2.0 has just been announced. While you’re at it. Also have a look at Freebases powerful API that provides access to an amazingly big community build ontology. You can play with it in the Query Editor.
Back on the original topic. There are some introduction videos on Google Refine online: