Atmel's ATMega328 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!

Documents: Atmel Datasheets

Feature Summary
- Program Memory Size  32KB (32K x 8) FLASH
- RAM Size    2K x 8
- 23 Number of I /O
- Package / Case    28-DIP (300 mil)
- Speed    20MHz
- EEPROM Size    1K x 8
- A/D 6x10b
- Operating Temperature    -40°C ~ 85°C
- Connectivity    I2C, SPI, UART/USART
- Peripherals    Brown-out Detect/Reset, POR, PWM, WDT
- Voltage - Supply (Vcc/Vdd)    1.8 V ~ 5.5 V
- Lead Free Status    Lead Free
- RoHS Status    RoHS Compliant