In my roamings, I have come across many a hexadecimal color-picker on the Internet. Most of them let you choose one of the 214 "web-safe" colors, and as such, are about as useful to me as a box of rocks. (Thanks, Greyson, for moving the box of rocks for me!) I stopped using the 214 colors when I got a color monitor that could show millions of colors. Usually, I just use the built-in color picker in whatever I'm using to make web graphics, either Photoshop, or Dreamweaver.
But lately, I have been returning to my roots and coding a lot of my html and css by hand, without special software, and usually remotely (with just a web browser). So I've been using a web-based tool that's pretty good. It is the MediaGods RGB to HEX color picker and it works pretty well.
But the other day, I found the most awesomest hex color picker on the Internet. These are the Hex Color Chips at december.com and with a good scroll wheel on your mouse, it's the best way I've found to find different shades of a single color that look good together. It is inspired, and has made some of my sites much prettier.
And as you know, that's what I'm striving for here.