Except for low power I'd like to hear constraints which rule out ARM... Thats the whole beauty of today's world. You don't need to make do with crappy & slow architectures which are just in the way of getting work done. I have build projects around Z80 processors, 8051, Hitachi H8/300(0), 68HC11 and probably some others I have forgotten. Nowadays I can do 95% of the projects with ARM based controllers and if I need low power then I use an MSP430. Maybe some projects are so simple I could get away with PIC, AVR, Attiny but those don't give any financial advantage. In most cases using an ARM has other benefits like fast PWM which make life much easier and strongly reduce external component count. For one of my customers I have developed a keypad with touch sensors. Because I can sample and process at relatively high speed there are only a few capacitors on the board. All the signal processing (anti-aliasing filtering) is done inside an ARM controller. I started the design with an I2C adc and analog comparators but the ARM controller is cheaper than the I2C ADC alone and the software people have less work if the ARM controller can deliver the data in a form which is directly useable. Last but not least the ARM controller is perfectly happy with 1.8V.