CloudShot is a small and simple screen capture tool which can immediately upload your images to Dropbox, making it easy to share them online.
Once installed, using the program is as simple as pressing PrtSc. You can then click in a window to capture its contents, or capture any rectangular region you like. And by default the image is saved as a PNG file, and opened immediately in your default image editor.
CloudShot can easily be reconfigured to suit your needs, though. Open the Settings dialog and you can change the program's hotkey; prevent it opening each grab; have it start with Windows (or not), or set its default save format to JPG.
The really interesting option here is the ability to save images to your Dropbox account. Once you've set this up, pressing PrtSc and clicking in a window will automatically save the grab, upload it to your account, and copy the URL into your clipboard. If you need to share it with someone else, just paste it into an email, forum post, instant message or anything similar, and they'll be able to view it right away
And in a welcome bonus feature, the program even maintains a history of your last 4 grabs. Right-click its system tray icon, select Recent Shots, and you'll see thumbnail previews of each grab: just click one to open it in your image editor.
Note that CloudShot is supplied as a .application file which downloads further components from the developer's Codeplex website.