Change & Replace Family and/or Type Names - A Free Add-in from Case (Updated)
"This is a handy little tool that goes out and renames families and/or type names in your project model. Be careful though, because this version does not offer a means of isolating the renaming scope, it is all or none."
This free add-in may be downloaded from the Case Apps website.
Update 5/8/2016: CASE and the CASE Apps website are no more but, courtesy of WeWork, the CASE Apps are now open source. They may be accessed on GitHub.