Free GCC tool chains are present for the TI MSP430, TI Tiva Series C (Cortex M4) and also TI Hercules (Cortex M3) series. Apart from that I have tried STM32F4 series with GCC tool chains.

I have personally developed Bluetooth stack using the GCC tools for the MSP430 using the CC246x Bluetooth modules and it was a blast.

So you have a lot of options with free tool chains. I personally use only free toolchains on linux. It is the best development setup and you have a lot of options for debugging and tool development.