I needed a simplifed way to do the kind of rapid imagesharing Mac-fans are doing with Skitch, but I don't have a Mac. What I do have is Windows, perl and imagemagick - so I wrote grab, a really simple script. It takes a bitmap image from the clipboard, converts it to a PNG, and copies the filename of the PNG to the clipboard, so it's easy to upload to your blog/image sharing service.
For cropping I just "Windows-key+R mspaint" and use the cropping tool and Ctrl-C - but I used to have this really nice tray app that could crop and clip in one go. I forgot the name, maybe Morten remembers.