Greasemonkey script decodes an impressive list of TinyURLs
Although the name of the script contains "TinyURL," that's not the only service it works with. It can decode dozens of different flavors of shortened links. I'm impressed with the huge number of services this plugin includes, from the very popular (the aforementioned TinyURL) to the obscure (PeaUrl). Installing it should leave you well-situated to know where these sometimes-sketchy links are taking you.