If you ever need to make changes to your database, but are afraid to mess with data stored in serialized arrays. Interconnect/IT’s Database Search and Replace Script in PHP is the tool for you. It’s an extremely powerful tool that will make a snap of performing search and replace actions on your WordPress databases.

Be warned, part of its ease of use can come back to bite you if an unauthorized user gets access this script. We recommend renaming the directory right after you extract the files. And most definitely delete the script when you’re done, or you’ll probably end up regretting it.

https://interconnectit.com/products/search-and-replace-for-wordpress-databases/

Update: Apparently too many people were not heeding the warnings and then whining to Interconnect/IT about their site getting hacked. You can no longer download the script directly from their site. You now have to sign your life away and be emailed a download link.