I would suggest a TI product. The MSP430, a low power microcontroller, combined with their transceiver line gives you:
These chips can be very very effective. I currently use the CC1100 and the MSP430 and we have been wanting to make a hardware revision to switch to one of these very tiny SoC. They have AES support in most of them. TI has a zigbee stack available also, allowing you to plug-n-play-n-sell.
You will get many extra pins, ADC, SPI/I2C, UART. These chips can be the core of an overall system and add transceiver.