There are a number of options, look at the products section!.
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Wifi Shield (Warning this is not compatible with the standard motor shield or with the standard servo lib.
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Wireless/SD shield with a WiFly module (Google). If you use this with a motor shield you can't use the the SD card feature.
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XBee shield (Zigbee) with WiFly module.
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2/3 above using XBee. To use and XBee you need a second attached to the PC.
Note that the motor shield and the standard servo lib are not compatible.
Options 2/3 above allow you to go to remote operation from control over the USB without code changes.
Mark