http://speckyboy.com/2009/02/16/32-indispensable-bookmarklets-for-web-developers-and-designers/

32 Indispensable Bookmarklets for Web Developers and Designers

All of these bookmarklets/favelets will be useful to all web designers and developers, they are the quickest method for testing, analyzing and tweaking any web page.
A Bookmarklet or Favelet is a small application tool, stored as the URL of a bookmark in a web browser or as a hyperlink on a web page.
To use these bookmarklets you can drag and drop the links to your Bookmark Toolbar or right click and save link as, this way you will always have quick access to these great tools