With flash memory being quite affordable these days, I decided to opt for a more spacious 32GB SD for my Pi as it ended running me only like $20. Possibilities for projects were already endless for this popular board and all that extra space got me thinking. Why not boot different distros?
A quick search led me to BerryBoot (currently version 2.0 as of writing) - it's an intuitive bootloader and installer combo done with Qt. All you need to do is make sure that your card is formatted as FAT then it's a matter of extracting the files. There's also an option to install OS images from the Internet (provided by the author), but they aren't the latest revisions so that's where the custom install option comes in.
You can pick any OS for the Pi that's in ".img" format then it needs to be converted into SquashFS format for the BerryBoot bootloader to accept it. Some things to note are that this can't be done on an image file that's on the same partition of the main OS install and although a majority of tailored images will work, you should be careful with how they're set up (e.g. Raspbmc). The aforementioned example actually sets up new partitions and will cause problems with BerryBoot and how it configures its structure.
I've converted two images including the latest official Raspbian "wheezy" (2013-02-09) distro and a security spin, PwnPi (version 3.0). You can download them via the following links or follow these steps to convert your own.