So called url shortening services such as tinyurl or bit.ly turn a lengthy url into a smaller one that redirects to the original destination. This is handy in several situations, but especially when text is either limited (like on Twitter) or difficult to enter.
The main problem that users have with those services is that the real destination is not revealed directly as the short URL does not reveal anything about the actual destination.
This is for instance exploited by users with malicious intent; while users might identify a target link as malicious or at least problematic, they might not be able to tell from looking at the short URL.
Untiny is a service that can display the final destination of dozens of url shortening services. This is in particular interesting since the developers have produced a variety of tools to use their service. Tools offered range from a web form on their website over browser plugins to userscripts and bookmarklets.
The tool collection is listed on the extra page of the Unity website. Each tool is linked from that page.
Untiny is for instance available as a Firefox add-on, Google Chrome extension, Opera widget, bookmarklet or Greasemonkey userscript.
The userscript will for instance convert all urls from supported url shortening services to the link destination, so that the real destination is shown on the website. Works perfectly fine on Twitter to increase the security on the Internet.
The wide range of tools for all popular browsers and other programs makes Untiny one of the best solutions to reveal shortened url destinations.
Update: The add-on has been discontinued. A solid alternative is the Firefox add-on Long URL please.
Update 2: Recent versions of Firefox do not seem to be compatible anymore with Long URL Please. A workaround at the time of writing is to install version .44 of the add-on which appears to be working.
Update 3: Long URL Please is no longer compatible with Firefox. You may try Simple URL Extender instead which requires that you right-click on links to reveal the final destination. Also, there is Long URL Please Mod which is a modification of the original Long URL Please extension.