Creating a Raspberry Pi SD card Image

The default Raspbian image from the Raspberry Pi website is set up for a UK keyboard, and is missing some software I want to use in school. So what I have been doing is installing Raspbian on one SD card, tweaking it to my liking, and then making an image from that card, which I can write to SD cards for students. Since our cards are 8GB, this technique saves a lot of time when you have many cards to write, since it only copies occupied sectors to the image, and not the whole card.