This blog post provides top 25 arduino projects

Color sorting robot using arduino

Arduino based distance meter using Ultrasonic sensor

Arduino radar

Arduino based Line following robot

Gesture control robot using arduino

Arduino robotic arm

Wifi control robot using Arduino

Weather Station using Arduino

Arduino sound controlled dustbin

DC motor control using arduino

Servo control using Arduino

Plant watering system using arduino

Digital alarm clock

Fast finger detection using Arduino

Home automation using arduino

Android control robot

Arduino based IC Tester

Finger print door lock using arduino

Face recognition based arduino door lock

Face tracking using arduino

Arduino control robot using matlab

Gas monitoring system using arduino

Tank level monitoring using arduino

Arduino based data logging

Baby monitoring using arduino