Windows: IrfanView has long been the small, efficient multi-tool for viewing and editing images on Windows systems. Its latest update adds to its surprisingly strong screenshot capture powers, along with updating a whole host of helpful image editing plug-ins.
The most obvious and notable new feature of IrfanView is its ability to capture whatever windows you've selected and automatically scroll their whole vertical length. It doesn't always work, but when it does, it saves you the aggravation of capturing multiple screens and pasting them together. It's also added helpful features like batch converting images to PDF files, framing images, and many, many more changes and updates, including updates to plug-ins.
IrfanView is a free download for Windows — be sure to watch during installation, though, as it may automatically install the Google Toolbar for your browser. If you've got a favourite use of IrfanView that you haven't seen highlighted, tell us about it in the comments.