Some of the useful sites I've found

Paint.net

Full featured drawing program, easy to use and very powerful.



Color-hex

Pick a color and it shows info and related colors.



CSS-TRICKS CSS Button Maker

One of the best all CSS button makers.
CSS buttons don't use an image they are pure code.



Gradient Animator

Makes a moving screen background from 2 or more colors.



Bezier Curve Tester

Tests custom timing curves for your animations

 

CSS3 GENERATOR

Explore basic css effects.



Hand Brake

Converts most any video format to MP4, does really good file compression.



CSSReflex Filter Effects

Brightness, Invert, Hue-rotate and many more.