There seem to be more and more options, yet they're never easy to find in stores. Nevermind that; the online places and some larger brick and mortars do have a small selection.
I used a Wolverine FlashPac 7100 (100GB) for about a year. It is as simple as can be; put the card in it, turn it on, press copy, come back later. It's not very fast; about 5mb/sec, in my experience. But it works reliably, runs on batteries as well as AC, and is pretty compact.
Looking at the Wolverine Data website, I see that they have a slew of newer models available; some with a picture viewer, some without, all faster than my old FlashPac.
Now I have a Sanho Hyperdrive Colorspace O (SATA version). It has a 500GB drive in it, and a color screen for viewing photos. It's much, much faster than the Wolverine, though a little larger. Battery life seems better too.
My father has an Epson P-2000. The Epson P-n000 series (2000, 3000, 4000, 5000, etc) spans several model years, and a variety of capacities. These units rank among the most expensive in price per gigabyte of storage, but do offer playback of audio and video in addition to photos. They seem to have one of the better user interfaces.
At any rate, I'm very happy with my Hyperdrive Colorspace. With a fast memory card, it can download about 1GB per minute. It works as a normal USB hard drive when plugged into the computer. It also allows files to be read AND written to the memory cards, though it does not function as a card reader while plugged into the computer (apparently that would hamper the read/write speeds too much. If I could choose any drive, it would be either the Colorspace O, or the highest capacity Epson model, at about twice the price for half the capacity (an exaggeration, but not by much).
