Hard to single out one as a favorite, since so much depends on the power/memory/peripheral tradeoff for each project. I recently used the TI/Luminary LM3S8962

Hard to single out one as a favorite, since so much depends on the power/memory/peripheral tradeoff for each project. I recently used the TI/Luminary LM3S8962 (ARM Cortex-M3 cpu). Loved it. No goofy pin multiplexing, GCC, easy to use serial bootloader, lots of horsepower, great peripheral mix. Interrupt system much more logical than ARM7TDMI. NXP LPC2106, not a bad chip, but better alternatives exist today. Too many power rails (core and I/O), limited interrupt system. Good tools, serial loader, plenty of memory on chip. Renasas/Hitachi H8 series. Actually a 16 bit chip. Dirt cheap in some variants (but way too many variants to pick from!). CISC with good code density, decent low power (forgiving power supply requirements, too), good GCC port. Serial bootloader is a bit crufty, a few peripheral bugs, translated documentation. Freescale MC68332: great chip, but it's technically a microprocessor (no onboard flash, at least in versions available to those of us that don't work for Government Motors...). It also includes the magnificent TPU (time processing unit), a work of art that's a subject all by itself. Long in the tooth but still soldiering on in many industrial applications.