People are starting to look seriously at the iPhone 4 as a robotics controller. It's got a full IMU and otherwise looks appealing. You can get all the hardware chip and sensor specs from this excellent iFixIt teardown, but here's just one example: the GPS chip.
It's a Broadcom chip and the refresh rate is "up to 2Hz". The user-accessible data is provided by the OS so the refresh rate in practice may vary, but the hardware looks pretty promising.