How to start with ARM development in Ubuntu?

GNU Toolchain for ARM Processors ( Download Link )

CodeSourcery, in partnership with ARM, Ltd., develops improvements to the GNU Toolchain for ARM processors and provides regular, validated releases of the GNU Toolchain. Sourcery CodeBench Lite Edition supports ARM, Thumb, and Thumb-2 compilation for all architectures in active use, including Version 7 of the ARM Architecture.

Alternate solutions, restricting oneself to software in the archive, include either using Ubuntu armel and native compilation (if one has compatible hardware), or using the gcc-armel-cross environment, running the results natively or in qemu. Although work is in progress, neither is truly suitable for embedded development at this time.