Just plug in a µSD card, add some speakers, upload the example code, and you can make your very own MP3 Playing Music Box

MP3 Player Shield - Turn your Arduino into an MP3 player.

With a GPS Shield, your Arduino will always know where it is.

GPS Shield - GPS isn't as complicated as you might think.

Cellular Shield w/ SM5100B - Turn your Arduino into a cellular phone! Send SMS text messages, or hook up a microphone and speaker and use it to replace your iPhone.

You could use an XBee to wirelessly trigger coffee machines, sprinklers, lights, or other household appliances.

XBee Shield - XBee's won't get you connected to the Internet, but they do provide a solid, cheap means for communicating wirelessly.

This is probably the least expensive WiFi-enabling Arduino shield.

Electric Imp Shield - Electric Imp is a unique WiFi module, which looks like an SD card, but it packs a powerful cloud-based WiFi controller.

This shield can get your Arduino connected to a WiFi router, so it can host webpages and scour the Internet.

Arduino Wi-Fi Shield - This is the Arduino Ethernet Shield sans wires.

Then it can act as either a web server, client, or both.

WiFly Shield - SparkFun's WiFi Shield mainstay, this shield equips your Arduino with the ability to connect to 802.11b/g wireless networks.

There's a great library to support it as well. The Ethernet Shield supplies your Arduino with an ability to connect to the world wide web.

Arduino Ethernet Shield - This is one of the more classic shields.

microSD Shield - The Arduino has limited storage space, but this easy-to-use shield (along with the SD library) allow for plenty of extra storage.

With a joystick and four buttons, this makes for a great robot controller.

Joystick Shield Kit - This makes your Arduino a bare-bones controller.

Great for learning the ins and outs of Arduino or incorporating into audio mixing projects. Danger Shield - The most awesomest shield evar! This shield is a crazy conglomeration of displays, potentiometers, and other sensors.LiPower Shield - This shield allows you to power your Arduino with a Lithium Polymer battery.It swaps the pins of the top shield, so they don't interfere with each other.

Go-Between Shield - The intention of this shield is to sit in between two shields.

Handy for connecting to external motors or heavy-duty sensors.

ProtoScrew Shield - Like the ProtoShield, but each pin is also broken out to a screw terminal.

Arduino wifi shield