The MSP430 is a quite new 16 Bit microcontroller from Texas Instruments. It has been designed for a very low current consumption, which is very useful for battery driven devices. There are different types with 1 to 60kB Flash, 256 to 2048B RAM, with or without hardware multiplier, UART or ADC, all in SMD package with 20 to >100 pins. The MSP430F1121 for example has 4kB Flash, 256B RAM, 2 timers and is in a SO-20 package.
Development hardware
Olimex sells very cheap adapter boards and programmers for MSP430 controllers. A board with the MSP430F1121 costs $7, the JTAG programmer $10. Together with the free software (C-Spy, mspgcc) you get everything needed for MSP430 development for less than $20.
Power supply
The MSP430 needs between 1,8 und 3,6 V. The following schematic shows a regulated power supply that can be used:
To the input you can connect a wall plug-in power supply, the output voltage of the circuit is regulated with the potentiometer.
Software
The software you need for the MSP430 is completely free. With the compiler MSPGCC, the debugging program GDB/Insight and a text editor of your choice you can write and compile C programs, program them into the controller and debug them.