I like having external hard drives, however, I have moved away from ones like the WD Passport and Seagate ones for several reasons.

They corrupt easily in my experience. They are partitioned from the factory with proprietary tools and software for recovery and backup that don't always work the way I WANT them to work. Finally, if something goes wrong, the drive is basically hosed. You can't open them without breaking them apart. I had to do that with a Seagate one recently unless of course I wanted to pay Seagate $50.00 for their recovery software or $200.00 to send them the drive for recovery.

These days, I get standard empty external cases. My current favorite is the OWC Mercury Elite Pro series:

http://ftp.macsales.com/shop/firewire/1394/USB/EliteAL/eSATA_FW800_FW400_USB

You can get them with hard drives or empty to use your own. They have USB 3.0 and USB 2.0 choices. If something goes wrong, you just open the case to deal with it. You decide how much space, and you are not forced to use a company's particular 'software solution' for backups, etc.

If your computer has PCI Express slots free, there are plenty of USB 3.0 adapter cards available. If you only have PCI, like I do in my older XP machine, there is one card that will give you USB 3.0.

http://www.startech.com/Cards-Adapters/USB-3.0/Cards/2-Port-PCI-SuperSpeed-USB-3-Card-Adapter~PCIUSB3S2

I currently have that Startech USB 3.0 card with the OWC Mercury Elite Pro with a 4TB hard drive for my music, movies, and TV show storage. It is working wonderfully with XP, 7, Linux, and Mac as it is formatted NTFS.

Unfortunately the external USB hard drives won't work with an iPad. You can not directly connect using the USB port of the iPad. You also run into issues with iTunes. There are external hard drives that use wireless adapters built in for iPads, or you can attach an external HD like the OWC one to a wireless hub like your router (if it supports it) or Airport base station. Then using an app called FileBrowser, you can view and use files from it. You could also share it using AirPlayIt HD on both the XP machine with the USB HD and the iPad.

Hope this helps.

I don't use their backup software. In my experience about 80% of the external drives that are no longer recognized by the computer are fine. What craps is the interface between the drive and the USB.

That crap interface between the drive and USB, if it dies, makes the WD and Seagate's unusable because they seal the drive in. That is why I now use external cases where I can easily access the drive. If the interface breaks, I just need to replace the case, not the drive, and no data is lost.

I purchased a SSD for my laptop and used the old drive as a 250 GB external HHD. I paid $7 for a case for the old 2.5" drive like the one below and formatted the old laptop HHD.
http://www.newegg.com/Product/Product.aspx?Item=9SIA1DS0JJ2628
I keep it in my router and can access it as a shared drive with any of our devices via our home wifi. I take it down when I travel or when I have a lot of stuff to move at once.

Seagate makes an energy efficient and very quiet drive. Some of mine are 10 years old and still going strong. The new ones are really small and a lot quieter. Get a Belkin USB hub to link them in. I've got three of them. They chain, and stack, so you can get up to 127 drives hooked into them if you want. I don't need that many (yet).