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Google now has its own URL Shortener for use with Google products. It is not currently available for broad consumer end use.  Here is the announcement on Google’s blog:
Making URLs shorter for Google Toolbar and FeedBurner

A longtime user of Tiny URL, Brendon Sinclair, the editor of SitePoint’s Tribune newsletter has mentioned a newer URL trimming service called Tr.im. In his opinion it is a better service than the venerable Tiny URL. See his mention in the Tips and Tricks section of the April 23 edition of the Tribune.