ST has a very nice "Standard Peripheries Library" for their STM32 ARM Cortex M3 line which abstracts all the bit and register manipulation away in a very elegant manner.
Atmel has the "AVR Software Framework" which I have heard good things about but haven't used it myself.
Nearly all the chip manufacturers I know of have some sort of framework/library for their Cortex M3 line (which is what is in the new Arduino).
TI started one for its MSP430's called Grace this summer, but it's very very primitive thus far.
Atmel also has one called FLIP for its USB-enabled MCU's to make them act as various USB profiles/devices.