An article like this could go on forever. People should comment with their favorites!
Here is a collection of animations you can quickly use in a project:
Beautify many types of code:
Generate sprites:
http://spritegen.website-performance.org/
Extract CSS data from HTML:
http://extractcss.com/
If you want to try wireframing/mockups, check this one out:
https://moqups.com/#!/