for the home solution i had a WD my book live?. plugs into the router and shares it through the wifi
i now have a HTPC so dont need the my book anymore
some routers also have a usb port to connect hdds to share through the network
as for a portable solution theres no real great solution except for micro sd/ usb sticks as any other form of hard drive requires power and as the ipad doesnt even have a usb port your stuffed anyway
i have an acer w510 it comes with 64gb and has a usb and micro sd slot. nice tablet but needs to be thought out a bit more
Bman,
the Seagate Wireless drive is pretty darn portable as it's only 2.5" drive. It runs off it's own battery power for up to 10hrs and you can recharge it from a battery pack or mains power.
As it's wireless an iPad can talk to it.
Voila portable and doesn't need usb.