This Atmel Atmega328P-PU is a 28 pin dip skinny package of an 8 bit microcontroller AVR with 32K of system programmable Flash.
Atmel's ATMega328P 8-Bit Processor in 28 pin DIP package. It's like the ATmega168, with double the flash space. 32K of program space. 23 I/O lines, 6 of which are channels for the 10-bit ADC. Runs up to 20MHz with external crystal. Package can be programmed in circuit. 1.8V to 5V operating voltage!
Tutorial on using ATmega328P-PU with low power goto SparkFun.com/tutorials/309.