0to255 lets you select matching colors for CSS, fast
0to255 it a very slick, well-designed tool for quickly finding color variations for borders and color gradients.
You dial in a Hex color code (say, "de40d5") and instantly get a long palette with light-to-dark variations of that particular hue. Every variation has its hex color value written across it, and when you hover over it you get a small swatch showing your original color along with the currently selected color, so you can see at a glance what they look like when paired.
The tool is obviously aimed at CSS-wielding web designers; it's not a substitute for anything Photoshop (or GIMP) can do in the color-matching department, but when you need to find a matching hue in a hurry, it's a very nice solution. If you click the de40d5 link above, you will see that you can provide the initial hue directly via the URL itself (meaning, you append the hue to "0to255.com/"). Slick, simple and effective.