I was trying to put together a nice background gradient in CSS that uses alpha values in the color to indicate transparency. There are a handful of tools out there that do it, but The Ultimate CSS Gradient Editor  has everything I needed:

The Ultimate CSS Gradient Editor was created by Alex Sirota (iosart). If you like this tool, check out ColorZilla for more advanced tools such as eyedroppers, color pickers, palette editors and website analyzers.

From Ultimate CSS Gradient Generator

Color pickers, sliders for positioning colors within the gradient, presets, a preview and a simple copy to paste output. All that, and it supports transparent colors in the gradient. Very nice.