Electric, Motor 9V Power Functions Servo with Dark Bluish Gray Bottom : Part 99498c01 | BrickLink
RUIZHI Lego Steering Servo Motor Servo Motor Blocks, Servo Motor Function Power Function Accessories with 15 Fixed Positions for Lego Technology Series 88004 : Amazon.de: Toys
Plastic Micro Servo Adapter for LEGO Cross - 16mm long : ID 4252 : $0.75 : Adafruit Industries, Unique & fun DIY electronics and kits
Geekservo 9g 360° Servo (compatible with LEGO) - RobotShop