Is it possible to have additional storage added to a 16GB iPad?

Not without selling it and buying a larger one.

(66648)

Move all your document, music, pictures and video to Dropbox, Box.com or Sugarsync. You'll get 2GB to 5GB free.

There are some wireless external hard drives that can be used with the iPad.

The Kingston Wi-Drive, which costs $50 for the 16 Gigabyte, and then $30 more for every 16 gigs more. It works by you turning it on and then accessing the files on it from an app that you download on your iDevice. You can access music, movies, and other stuff. No connections or anything, it works like a WiFi connection, you connect to it from the setting on the iPad under wireless networks.

Then there is the Seagate GoFlex, which some would recommend over the Wi-Drive. But this one costs $199 and had 500 Gigabytes of storage. It works the sameway as the Kingston: no wires, runs over its wireless connection. You can actually fit up to 300 HD movies on it.

Another option:

Expand your iPad's storage capacity with HyperDrive

http://www.macworld.com/article/1153935/hyperdrive.html

On the road with a camera, an iPad, and a Hyperdrive

http://www.macworld.com/article/1160231/ipadhyperdrive.html

 Cheers, Tom 😉