This is how to hack an Evil Mad Scientists Lab Arduino ISP Shield so that you can use the Arduino environment to program some nifty little microcontrollers.
The Arduino is a great little development environment for creating electronic projects http://www.arduino.cc/ but there are times when you just want the minimum possible pieces, and don't want the expense, or size, of a full Arduino plus breadboard/prototyping shield.
That's when you want to use a dinky microcontroller.
Fortunately AtMel (who make the AtMega inside the Arduino) also make a bunch of little ones called AtTiny. These range from 6 pin to 28 pin chips, and use almost the same instruction set as the big guys - they are part of the same AVR family.
My chip of choice for these kinds of projects is the ATtiny85
It has 8K of program memory, comes in a PDIP 8 pin package and has 5 (or 6) I/O pins. It also has 512 bytes of static RAM, and 512 bytes of EEPROM. It can run on two AA batteries (3 Volts, some version will go as low a 1.8V), and doesn't use much power.
For the technically inclined see http://www.atmel.com/dyn/resources/prod_documents/2586S.pdf for a summary of its capabilities.