OE/Yocto prebuilt toolchains
Yocto Project pre-built toolchains
This site provides a large number of ready-to-use cross-compilation toolchains, targetting the Linux operating system on a large number of architectures.
Get the appropriate Openembedded/Yocto toolchain here : http://downloads.yoctoproject.org/releases/yocto, and execute the shell script to install them into (by default) /opt/poky/. Once that's done, extend your search path to pick up both the cross-compile utilities, and some additional Yocto utilities as well.
Most toolchains are tested by building a Linux kernel and Linux userspace, and booting it under Qemu. This is of course not possible on some CPU architectures.