Debian “squeeze”
If you’re just starting out, this is the image we recommend you use. It’s a reference root filesystem from Gray and Dom, containing LXDE, Midori, development tools and example source code for multimedia functions.
Arch Linux ARM
Arch Linux ARM is based on Arch Linux, which aims for simplicity and full control to the end user. Note that this distribution may not be suitable for beginners.
QtonPi
QtonPi is an Embedded Linux platform plus SDK optimized for developing and running Qt 5 Apps on Raspberry Pi. More information is available here.