Wireless Storage

There are an increasing number of products on the market that allow you to store video, music, photos and other files externally to the iPad. You can then access them wirelessly via an app on your iPad, Kindle or Android device. They all have inbuilt rechargeable batteries of varying capacities and can be charged whilst in use. Video playback is performed by your device's media player which for Apple means that only mp4 files will work unless you download an alternative such as AVPlayerHD, GoodPlayer or CineXPlayer.

Gaunlet
Apotop Wireless Card Reader - £50
Easily transfer and view photos, documents and video via Wi-Fi on any device from a USB stick or SD Card. Share media contents over Wi-Fi to 3 users simultaneously. Watch this video of the Apotop in operation. Battery life of 3 hrs and can be charged via usb.

Main advantage - Cheapest and flexible.

Gaunlet
Patriot Gauntlet Node HDD Wireless Enclosure - £100
The Gauntlet lets you take any laptop size (2.5") hard drive up to 2TB and turn it into a completely portable wireless storage solution for tablets and smart phones. Wirelessly share and stream movies, music and documents with up to 8 devices simultaneously. Supports NTFS, so file size is not limited to 4GB. You will need to already own or purchase a separate hard drive. Battery life of 3-5 hrs.

Main advantage - Biggest potential storage space.

Airstash
Maxell Airstash Wireless Drive - £90
Portable Private Wireless Network Drive with a slot for SD cards up to 128GB. Comes with an 8 or 16 GB SD card. Only supports FAT32 so file size is limited to 4GB. Can convert RAW camera files to jpegs. Review from the Gadget Show - http://gadgetshow.channel5.com/gadgets/maxell-airstash
Battery life - 6 hrs.

Main advantage - Smallest.

SD
Kingston wi-Drive - £90 to £150
Portable Flash-based storage that comes in 32, 64 and 128 GB models (FAT32). You can bridge the wifi connection which enables you to surf the Internet and watch films at the same time if you wish. Allows 3 users to connect to it and view different media at the same time. Nice looking but seems expensive for rather limited storage. It also breaks connection when charging from a PC. Battery life of 5 hrs.

Main advantage - All-in-one product.

SD
iUSBport (formerly cloudFTP) - £100
Plug any USB device into this and it makes the devices contents (music, video) available to ANY wireless device. Instantly stream 3 different HD movies to 3 different devices or perform 2-way file transfer with up to 8 different devices. iUSBport is pocket size and battery operated so you can carry it where ever you go. Watch this video of the hyperdrive in operation. You will need to already own or purchase a separate usb flash or hard drive. Battery life - 4 hrs.

Main advantage - Most flexible.

SD
Seagate GoFlex Satellite - £170
Most expensive option, but the latest model comes with a massive 1TB (1000GB) of storage. Battery life of up to 10 hrs.

Main advantage - Biggest out of the box storage capacity.