[nmjohn]

Amazons URL's are actually quite interesting -

    Original: 
        http://www.amazon.com/Structure-Interpretation-Computer-Programs-Engineering/dp/0262510871/

    Equivalent:
        http://www.amazon.com/dp/0262510871
        http://www.amazon.com/dp/0262510871/something-else
        http://www.amazon.com/something/dp/0262510871
        http://www.amazon.com/something/dp/0262510871/something-else

It appears so long as 'dp/0262510871' is in the url (without dp/# appearing before it, but a second one after is fine) it works.

[cpeterso]

Or simply http://amzn.com/0262510871

[rawdisk]

HTTP/1.1 301 Moved Permanently

This is a URL shortener that just redirects to the full URL that has same number. Easier to type but otherwise acomplishes nothing. Server with the content still needs full URL. All this shorter URL gets you is the full URL.