On Windows PC's I use SnagIt from TechSmith for screencaptures etc. On OSX I use the built-in capabilities of OSX for capturing screens, windows, or areas, but there was something missing...
SnagIt can capture large windows within *cough*Internet Explorer*cough* or Firefox as one image. So no need for a capture, scroll down, capture again etc. This feature isn't available in OSX, or any (commercial) capturing software I could get my hands on. Until I ran into Screengrab.
Screengrab is a FireFox extension which allows you to save an entire webpage as an image (jpg or png). Excellent extension if I may say so.