Arduino Micro Pro R3, BreadFruit Electronics

The Arduino Micro is essentially a shrunk-down (1.9″ × 0.7″) version of the Arduino Leonardo: it is a microcontroller board based on the ATmega32U4 running at 16 MHz with 24 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs). This board ships with the male header pins soldered in.

3-Pack Arduino Pro Micro 3.3V from ElectricDream on Tindie

3.3V Arduino compatible Pro Micro

ElectroCookie Solderable Breadboard PCB Board for Electronics Projects Compatible for DIY Arduino Soldering Projects, Gold-Plated (9 Pack + 3 Mini, Multicolor Pack) : Industrial & Scientific

Arduino Pro Mini, BreadFruit Electronics

The Pro Micro is similar to the Pro Mini, except for the fact that it utilises the ATMega32U4. Additionally, there is an on-board USB transceiver

3.3V Arduino compatible Pro Micro

Arduino Pro Mini, BreadFruit Electronics

Arduino Micro with Headers - 5V 16MHz - (ATmega32u4 - assembled) : ID 1086 : $24.95 : Adafruit Industries, Unique & fun DIY electronics and kits

x3 pcs 3.3V Pro Micro

3-Pack Arduino Pro Micro 3.3V

running at 5V/16MHz Supported under IDE v1.0.1 On-Board micro-USB connector for programming 4 x 10-bit ADC pins 12 x Digital I/Os

OSOYOO Pro Micro 5V/16MHz Module Board with 2 Row pin Header Replace wit Pro Mini for Arduino