Cortex-M3 aka CM3 based MCUs are getting more and more popular
TI has just acuired LuminaryMicro with their entire portfolio of CM3 based micros.
TI Stellaris page link

STMicro has published introductory "STM32F10xxx Cortex-M3 programming manual" click on the link to access PDF document. 

 NXP has "Introduction to NXP's new LPC1700 Cortex-M3 Microcontroller" webinar and offers free LPC1766
samples on this page http://response.nxp.com/forms/experience_mcuoptions 

NXP will be the first to release MCUs based on ARM 's newest core Cortex-M0.
ARM IQ magazine from March 2009  has number of good articles about CM0
and NXPs LPC1100 series