The official ARM cross-compilation toolchain
https://launchpad.net/gcc-arm-embedded

# add-apt-repository ppa:terry.guo/gcc-arm-embedded
# apt-get update
# apt-get install gcc-arm-none-eabi

If no package can be found, then change "raring" to "precise" in
/etc/apt/sources.list.d/terry_guo-gcc-arm-embedded-raring.list