It was bound to happen. Microcontrollers are getting so tiny, they're hard to find. Microchip's latest, the 1-MIPS PIC10F line, fits into a small SOT-23 package. Using an on-chip, 4-MHz oscillator (1% accuracy), the six-pin PIC10F provides four I/O pins, using the remaining two for power and ground. It's tough to get much tinier than this.
Price-wise, the PIC10F is small as well, coming in at $0.49. For less than four bits, you get 16 bytes of RAM and 256 12-bit words of flash memory. It has a two-level hardware stack, an 8-bit timer, an 8-bit prescaler, and an optional analog comparator with an on-chip voltage reference. Versions are available with twice as much RAM and flash memory. That may not sound like much, but it's more than enough for most target applications.
The maximum power draw for these chips is under 2 mA. Standby mode only draws 100 nA. Input pullups are small to minimize power usage. Outputs can sink/source 25 mA per pin. This is more than enough to handle high-current LEDs.
Versions with industrial (−40°C to 80°C) and extended (−40°C to 125°C) temperature ranges are available. Operating voltage ranges from 2 to 5.5 V. The PIC10F supports In Circuit Serial Programming (ICSP). Versions are available for use with Microchip's development tools.
The PIC10F family will replace many discrete and logic functions, reducing the implementation to a single chip. It should offer an alternative to the way that designers think about solving a problem.