ZScreen is a powerful, open source screenshot app
ZScreen is an extremely flexible alternative. The usual capture options are supported - full screen, active window, or selection and hotkeys can be mapped to a single key or to two or three key combinations.
Handling options are numerous. You can capture to the clipboard, directly to a file, multiple FTP locations, or ImageShack. If you're like me and you need to edit your screenshots in another application (like Paint.net, the Gimp, or Photoshop) ZScreen can capture and instantly open the image in your favorite editor.
It also maintains a cache of your screenshots, saving even if your destination is the clipboard. Having ready access a history of recent captures in their original resolution is undeniably handy, and it eliminates the annoyance of your clipboard getting accidentally overwritten by another copy operation.
You're free to change the size and location of your cache folder, and file naming is extremely flexible. ZScreen can automatically add time and date elements, the active window title, autonumbering, and any custom text you choose.
Captures can be saved in six different image formats and ZScreen can fall back to another option when the file hits a certain size. I've set it to capture uncompressed PNG files up to 500k and then fall back to 90% JPG after that.
There are a few shortcomings, like the lack of a timer function and inability to capture scrolling regions, but it provides all the key features I'm looking for - and then some. ZScreen is free, open source, and runs on Windows only. .Net 2.0 is required.