The Pololu 3pi robot is a complete, high-performance mobile platform featuring two micro metal gearmotors, five reflectance sensors, an 8×2 character LCD, a buzzer, and three user pushbuttons, all connected to a C-programmable ATmega328 microcontroller.
Capable of speeds exceeding 3 feet per second, 3pi is a great first robot for ambitious beginners and a perfect second robot for those looking to move up from non-programmable or slower beginner robots.

The 3pi robot is designed to excel in line-following and maze-solving competitions and makes a great platform for people with C programming experience to learn robotics.
At its heart is an Atmel ATmega328 microcontroller running at 20 MHz with 32KB of flash program memory and 2KB data memory, enough space to run complicated programs.
An extra 512 bytes of persistent flash memory is provided on the microcontroller for data logging or long-term learning applications.
You can use AVR Studio or WinAVR for development. 
The 3pi is also compatible with the popular Arduino development environment.

Comes with 4 LEDs. Needs 4 AAA batteries, not included.
 

Features:

• ATMega328 Processor
• TB6612FNG Motor Driver
• 2 motor channels
• 3 - 7V operating voltage
• 80kHz max PWM fequency

Documents:

• User's Guide
• Quick Start
• Schematic
• Demo Hex File
• AVR C/C++ Library
• AVR C/C++ Library Commands
• Programming using Arduino 
• Wall Follower Example
• Radio Control Example
• Line Follower Example
• Motor Driver Example
• Spanish User's Guide
• 3pi Forum

Dimensions:

• 9.5 cm/3.7" diameter ("3 pi" diameter)
• 83 g/2.9 oz without batteries