Save as image - an aptly named Firefox plugin that lets you save a page, frame, or part of either as an image directly from Firefox.
Pearl Crescent Page Saver - Save images of web pages in jpg or png format; save the entire page or just a portion of it, with the ability to automatically scale the image to a smaller size.
Picnik for Firefox - if you use online image editor Picnik this Firefox plugin enables you to easily import a screenshot of the currently opened webpage into it.
Snissa - simple Firefox plugin for taking web page screenshots.
Screengrab! - a plugin that lets you save visible part of window, the entire page, just a selection, or a particular frame of a webpage.
ieSnapshotter - a shareware plugin for Internet Explorer that allows you to take screenshots and thumbnails of web pages.
SnagIt - definitely one of the best programs for screenshot capturing, with all the options you might need. Integrates with Firefox, can replace the standard Windows print screen function, and enables you to create profiles for various types of use. Costs 39.95 bucks, but you can try out a free trial version before buying.
FastStone Capture - a powerful utility for taking screenshots with a floating control panel as well as the ability to capture anything on the screen including windows, objects, full screen, rectangle regions, and even freehand-selected regions.
WebShot - a program that allows you to take screenshots and thumbnails of web pages or whole websites. Its main advantage is its powerful command line utility which enables you to automate the process of taking screenshots.
Paparazzi! - a tiny application for Mac OS X that lets you take screenshots of web pages.
PrintKey - replaces your print screen function with a better one with more features. There's a commercial version but you can also find an older, unsupported, freeware version on the provided link.
I4X Screencatcher - take screenshots of the active window, entire screen, or the selected area with this tool.
InstantShot - an advanced but freeware application for Mac OS X that sits in your menu bar and gives you a myriad of screen capturing options, including capturing a region, hotkeys, several output formats, image scaling and many others.
WebShotsPro - enter a URL address and get a screenshot of the website in question. Simple. You might encounter quite a long queue before getting your screenshot, though.
Thumbalizr - already mentioned in a recent article, Thumbalizr lets you create screenshots of websites by pasting their URL; the only problem is that it doesn't always work. (via)