CodeSourcery

GNU ARM toolchain

http://www.codesourcery.com/sgpp/lite/arm/portal/subscription?@template=lite

You'll probably want the EABI-targeted version:

http://www.codesourcery.com/sgpp/lite/arm/portal/release1294

Tested to work with Freescale MC13224v and Atmel AT91SAM7 chips.

Linux and Win32 support.

LostARM

GNU toolchain

http://lostarm.sourceforge.net/

Build-it-yourself toolchain. The project also includes a chip & board support package framework, and has some code for AT91SAM7 chips.

Linux only. Might built under Cygwin?

YAGARTO

GNU toolchain

http://www.yagarto.de/

Native Win32 GNU-based toolchain. Works very well, doesn't require cygwin. Limited makefile support.
The YAGARTO site has some great tutorials, like setting up Eclipse to work with an external Makefile project for ARM embedded targets.

An STM32 bootloader application, implemented in python: http://tuxotronic.org/wiki/projects/stm32loader
Current untested by us

LPCXpresso

See the linked page specific to building firmware for NXP LPCXpresso board.