Archive.org’s Wayback Machine is an incredible tool. Here’s how to use it more effectively.

Advanced search (with all options and handy tips):
http://web.archive.org/collections/web/advanced.html

Bookmarklet:
javascript:location.href='http://web.archive.org/web/*/'+document.location.href;
(copy and add as a new bookmark)

Or just type it by hand in the url bar. The syntax is as follows
http://web.archive.org/*/url