I was reading about the ATxmega16A4U here:
It looks like they might be available now for around $7 in a QFN44 package.
Sounds like a cool chip, 32 MHz, USB interface, AES encryption, 12 bit ADC converter (2 million per second), 12 bit DAC converter (1 million per second), Analog comparator, 5 x 16-bit timers/counters, IR module, CRC generator, you can generate a software reset (lol), DMA, capacitive touch sensing, interrupt priorities, 2 x SPI, 2 x I2C, 5 x USART, and so on.
But to play with one, you would need to be able to insert it into a breadboard. I have a QFN44 socket, but that just has pins on the bottom. Does anyone know of a breakout board that could be plugged into? Or would I end up soldering 44 pins to some kind of test headers?