ATmega328 is a very popular microcontroller. The processor has plenty of GPIO, analog inputs, hardware UART, SPI and I2C, timers and PWM galore - just enough for most simple projects.
Adafruit Metro Mini 328 - 5V 16MHz is the culmination of years of playing with AVRs: Adafruit wanted to make a tiny, breadboard-friendly development board that is easy to use and is hacker friendly. Metro Mini can be programmed with the Arduino IDE (select 'UNO' in the boards dropdown)
ATmega328 chip has 32KB of flash (1/2 K is reserved for the bootloader), 2KB of RAM, clocked at 16MHz. You can power Adafruit Metro Mini 328 - 5V 16MHz with 6-16V polarity protected on the Vin pin, or plug the micro USB connector to any 5V USB source.
Adafruit Metro Mini 328 - 5V 16MHz has 20 GPIO pins, 6 of which are Analog in as well, and 2 of which are reserved for the USB-serial converter. There are also 6 PWMs available on 3 timers (1 x 16-bit, 2 x 8-bit). There is a hardware SPI port, hardware I2C port and hardware UART to USB.
GPIO Logic level of the Metro is 5V but by cutting and soldering closed a jumper on the bottom, you can easily convert it to 3.3V logic. The board has 5V onboard regulator with 150mA out, 3.3V 50mA available via FTDI chip
There is a genuine FTDI hardware USB to Serial converter that can be used by any computer to listen/send data to the microcontroller and can also be used to launch and update code via the bootloader
Adafruit Metro Mini 328 - 5V 16MHz can be programmed easily, it comes pre-loaded with the Optiboot bootloader
Adafruit Web Site: http://www.adafruit.com/product/2590