CQRobot -Speaker 8 Ohm 3 Watt for Arduino, 2.54mm Dupont interface, it is ideal for a variety of small electronic projects. : Amazon.de: Electronics & Photo
Amazon.com : WINGONEER TPA3116 2X50W Bluetooth Digital Power Amplifier Board with Remote Control, Support FM Radio/TF Card/USB Recording Play 8~26V DC for Headphones HiFi Amplifier iPhone Home Theater : Electronics
Amazon.com: Ground Zero Iridium 16,5 cm / 6.5" Subwoofer - 4 Ohm - 100 WRMS : Electronics
Earthquake Sound MQB-1 Pro Low Frequency Effects Transducer : Everything Else - Amazon.com