When 17 microcontroller vendors pick your processor architecture, you have a right to sing “Something’s happening here.” Alban Rampon of ARM just published a blog entry titled “ARM Cortex-M—How could you choose your microcontroller?” This blog entry lists 17 semiconductor vendors incorporating the ARM Cortex-M family cores in their chips. The list includes: Fujitsu, Texas Instruments, Nuvoton, NXP, STMicroelectronics, Analog Devices, Atmel, Broadcom, Cypress Semiconductor, Dust Networks, Ember, Energy Micro, Freescale Semiconductor, Samsung, Toshiba, Triad Semiconductor, and ON Semiconductor. Now in reality, not all of the offerings from these vendors are microcontrollers. For example, Triad’s Mocha-1 is a gate array ASIC. Some of the parts from a few other vendors are perhaps more dedicated to a single purpose than befits a microcontroller. But there are at least a dozen bona fide microcontroller vendors in this list.
You should also read this blog entry for the discussion of development environments available.