The LittleArm is one of the most advanced Arduino robot kits on the market, and 1 of the easiest to start with. Using its desktop software this arduino arm can be trained like industrial arms or reprogrammed from scratch. The modifiable breadboard also allows expansion of the Littlearm arduino arm with sensors and other components. Despite its capabilities the LittleArm can be built and programmed by anyone from age 10 and up, making it ideal for STEM education
The Bioloid STEM is a kit that has 21 weeks of educational material around the seven robots you can build form it. The kit is good for teaching STEM from basic to advanced levels in topics ranging from electronics to programming. The kit is ideal if you are just getting started in robotics, adult or student.
Hexapod spider robots are a common in the Arduino maker space. But the Alum Allow Hexapod Spider is a special arduino kit because it's legs are among the most articulate. While it is a relatively complex and expensive kit it would be a fun arduino project.
This Arduino Crawling Quadruped Robot kit has everything you need to make a walking quadruped robot. Each leg has three joints driven by servos. Using the Sunfounder Mobile Robot Remote Controller can easily direct the robot in any direction. The kit uses the SunFounder Nano board as the main controller. A SunFounder Servo Control Board integreate the battery Nano, servo, and nRF2401 wireless module together.
While the this arduino robot kit is cool when it is done, it is fairly complex to build and is not recommended for beginners.
The Official Arduino Robot Kit had to be on this list. While soldering is required to put this robot kit together is is not a difficult robot kit. Once it is built just use a USB cable to connect the robot to the Arduino IDE on a desktop computer and download an example program. The robot comes with all kinds of integrated inputs: two potentiometers, five buttons, a digital compass, five floor sensors, and an SD card reader.