Ever had a long long long URL that you had to send out to a friend on IM or email? It was so long that it stopped being a URL? A good example of these types of URL are shopping site URLs.
Phew! That was long. You might already know a few sites like www.tinyurl.com that shorten/make tiny your long URLs. But here is a comparison of five of them that I found from this link.
Here is a comparison. I've put my Google Reader Shared Items as a test link.
Test link: http://www.google.com/reader/shared/15393105146633867508
Resulting Short links: (no. of characters excluding the 'http://')
looks like is.gd and bit.ly tie for the first position. Get more info by visiting the sites and reading the article linked.