Portable HD

If you are looking for portable storage, then you have to consider which size you are okay with. If you need something that is entirely powered from USB, then you are stuck with 2.5 inch drives which will offer okay performance but not as good as the 3.5 inch drives.

If you need to do a lot of work on the drives and do not need much storage, then you can go with a 2.5 inch enclosure, then buy a low cost 256GB SSD.

If you will have ample access to power outlets, then you can go for a 3.5 inch drive

Some decent drives are http://www.newegg.com/Product/Produc...82E16822178474

and if you have access to some electrical outlets, then http://www.newegg.com/Product/Produc...82E16822178354

PS old external drives can be upgraded. simply remove the casing and swap the drives.
(I do that with an old acom data branded external drive, I now use it as an esata dock when making backups (6 2TB drives that I cycle through for my manual backups)
http://i.imgur.com/zNvUIWM.jpg