You can get an air stash, which uses an SD card. It has a usb port. It has its own wifi so you can put the clips on the SD, put that in the Air stash, log into the Air stash, then play the clips. YOu can save photos to it and many apps can read/write from the device. It can be used with a laptop, Android or iOS device. This thing is super small and chargers on any usb charger.
Or you can a Gauntlet Node, which is also a wifi drive with similar features. You can install a 2.5 inch hard drive in this, so you can control the amount of storage you have.
Seagate makes a similar thing 500GB called a Goflex Satellite. They have a new 1TB drive on the market too. Kingston makes a similar device too (Wi-Drive?). There is also the iUSBport line of devices.
These types of devices are becoming the new thing for mobile device wifi storage. None of these are iPad specific (with the possible exception of the Kingston), by the way. It would be silly to do that since these are wifi devices. No reason to tie them to one platform.