When all you need is a few GPIOs this is just the chip for you. With 20Mhz speed, 8k of programmable memory, 512b In-system programmable EEPROM, 512b Internal SRAM, 6 IO pins (3 of which have PWM) this chip is fantastic for any projects that you just don't need 15-20 pins.
MIT High-Low Tech article on using the Arduino IDE to program uC from the ATtiny line. The high-performance, low-power Atmel 8-bit AVR RISC-based microcontroller combines 8KB ISP flash memory, 512B EEPROM, 512-Byte SRAM, 6 general purpose I/O lines, 32 general purpose working registers, one 8-bit timer/counter with compare modes, one 8-bit high speed timer/counter, USI, internal and external Interrupts, 4-channel 10-bit A/D converter, programmable watchdog timer with internal oscillator, three software selectable power saving modes, and debugWIRE for on-chip debugging. The device achieves a throughput of 20 MIPS at 20 MHz and operates between 2.7-5.5 volts.
Flash: 8KB
Pin Count: 8
Max. Operating Frequency: 20 MHz
CPU: 8-bit AVR
Max I/O Pins: 6
Ext Interrupts: 6
SPI: 1
I2C: 1
SRAM: 0.5KB
EEPROM: 512B
Temp Range (deg C): -40 to 85
Operating Voltage: 1.8 to 5.5
PWM Channels: 6