I came across a couple of these dev boards while organizing.http://www.ti.com/tool/msp-exp430fr5739
I picked up two of them when they were on sale for $15 (and free shipping!) and just now considered how awesome they are, especially when compared to Arduino boards (for clarity, I use Arduinos as dev boards and program in C/assembly. AVRs are awesome but the Arduino IDE is horrible.).
The uC is a 16-bit processor with an internal oscillator up to 24MHz (controllable from software). Interestingly, it uses 16kB of non-volatile FRAM for shared program memory and RAM, meaning that you'll probably have much more RAM available than the 2k on an ATMEGA328.
The board has two push-buttons and eight LEDs for UI and a 2-axis accelerometer and a thermistor already on there. There are pads for a 32.768kHz crystal if you want to do RTC stuff. And it has the hardware on there for programming (so no external programmer needed) and USB-UART.
So color me impressed (especially for $15). Now to come up with something to use them for...