I still don't understand why people are focused on PICs and AVRs. ARM has had better functionality and pricing (starting at the mid-range; low range is still dominated by 8-bit) and better peripherals for at least 5 years now.
TI Stellaris launchpad: $5, 80MHz, 32-bit ARM Cortex-M4 CPU with floating point, 256Kbytes of 100,000 write-erase cycle FLASH and many peripherals such as 1MSPS ADCs, eight UARTs, four SPIs, four I2Cs, USB & up to 27 timers, some configurable up to 64-bits. Integrated in-circuit debugger.
Each of the following also have an integrated in-circuit debugger which is compatible with OpenOCD
STM32F0DISCOVERY: $8 48MHz ARM Cortex-M0, 64 Kbytes of flash and 8 Kbytes of SRAM, standard communication interfaces (up to two I2Cs, two SPIs, one I2S, one HDMI CEC, and up to two USARTs), one 12-bit ADC, one 12-bit DAC, up to five general-purpose 16-bit timers, a 32-bit timer and an advanced-control PWM timer.
STM32VLDISCOVERY: $9.90 24MHz ARM Cortex-M3, 128KB Flash, 8KB SRAM, standard communication interfaces (up to two I2Cs, two SPIs, one HDMI CEC, and up to three USARTs), one 12-bit ADC, two 12-bit DACs, up to six general-purpose 16-bit timers and an advanced-control PWM timer.
STM32F3DISCOVERY: $10.90 72MHz ARM Cortex-M4, with FPU, 256KB Flash, 48KB SRAM, up to four fast 12-bit ADCs (5 Msps), up to seven comparators, up to four operational amplifiers, up to two DAC channels, a low-power RTC, up to five general-purpose 16-bit timers, one general-purpose 32-bit timer, and two timers dedicated to motor control. They also feature standard and advanced communication interfaces: up to two I2Cs, up to three SPIs (two SPIs are with multiplexed full-duplex I2Ss on STM32F303xB/STM32F303xC devices), three USARTs, up to two UARTs, CAN and USB. To achieve audio class accuracy, the I2S peripherals can be clocked via an external PLL.
STM32F4DISCOVERY: $14.90 168MHz ARM Cortex-M4 with FPU, 1MB Flash, 192KB SRAM, and way too many peripherals to list here.
All the above are supported by GCC and OpenOCD.
With prices, capability, and development tool support like that, why would you use an 8-bit micro? It doesn't give you the same support that Arduino does. You have to learn how the peripherals work and you have to write your own interfaces to things like ADCs, but the examples are pretty complete.