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.
Expand your iPad's storage capacity with HyperDrive
On the road with a camera, an iPad, and a Hyperdrive
I've been researching this as well and came across a couple things. One that turns any external HD into a iPad/iPhone/iTouch compatable external drive via wifi. I haven't purchased mine yet, but I am intrigued and probably will next paycheck.
The article which lead me to it:
And the company/product:
Any one have any hands on experience with these can weigh in with more veracity. Otherwise, after I figure it out I'll repost.
Please note this is copy and paste from another site, just trrying to help.
"I have an Airoort Extreme with two hard drives connected to it and I can access them directly from my iPad with a program called FileBrowser. Bought it awhile back but I'm pretty sure it was no more than a couple bucks. You open it up and just add a new connection with the name and IP address of the base station and when you connect the shared drive should come right up."
Works with your mac laptop/desktop, iPad and wifi connection.
Download AirPlayIt HD on both devices.
Start the app on both devices.
Add folders to be shared including EXTERNAL Hard Drives in Settings (of app).
Click on the Laptop/Desktop in the App on your iPad.
From there, you can access all of the files from your laptop/desktop on your iPad that you decided to share in the app on you laptop/desktop. I have it and can verify that I can watch video that has a resolution all the way up to 1080p on my iPad. It's quite simply the easiest way to stream audio/video to your iPad from external sources...
AND IT'S FREE!!!!!