Say you're taking a long trip, bringing a digital camera, you don't want to lug a laptop computer, and you don't want to lose the pictures you're taking. It may be a once-in-a-lifetime trip somewhere like a trip to Antarctica, or a 50th wedding anniversary, where losing the pictures you take means they cannot in any way shape or form ever be recaptured.
How much storage will you need? This question will determine which of the units you should buy. The answer is based on the number of pictures you'll take on your trip, and the size of each picture. If you're a snapaholic like me, this could run to several gigabytes. Especially with the large file size of current cameras. And why not be a snapaholic? It's just data, unlike the olden days when pictures were on film and you incurred a significant cost per picture.
Is multimedia important? Many of the devices double as MP3 or video/DVD players. The question in my mind is whether this is useful. Maybe you can avoid carrying two devices (e.g. an iPod plus a digital wallet) with a combo device, but I think the multimedia features are extraneous to photographers. On the other hand the complexity of gadgets is increasing. Many digital cameras now make decent movies or record audio.
Here's a few ideas to consider:
Bring extra memory cards: One of the simplest choices is to simply bring lots of memory cards. When you fill up one card, you find the next blank one and switch. With todays prices for memory cards it's quite affordable to do this. Further, memory cards have no moving parts, no delicate innards, and require no power to maintain them.
On the other hand this gives you a single point of failure. For example what if you somehow lose the cards?
Digital wallet: These gadgets hold a hard disk, accept memory cards, and automatically suck all photo's to the disk. The slim technical difference between these and iPods or other music devices means the market morphes some of them into multimedia gadgets.
You still have a single point of failure. What if you lose the gadget? Or, since it has a hard disk in it, what if the disk breaks or has another failure? The gadget is also going to require power, and what if you're traveling to foreign lands? (e.g. you'll need power adapters) But what if you're in the field, run out of memory cards, and run out of power in the gadget, and you're facing the most beautiful scene ever? Maybe some scenes were meant to remain unphotographed?
[adorama:ICDITB40|Adorama Image Tank, Portable 40 GB Hard Disk for Image Downloading and Storage, with Rechargable Battery & Charger] A dedicated wallet device.
Jobo Giga One, 80 GB Portable Storage Device with USB 2.0 Interface A dedicated wallet device.
Jobo Giga Vu Pro External Storage Device and Media Player with 120 gb Hard Drive A digital wallet meant for professional photographers. For example it supports viewing RAW photos on the included screen, as well as JPEG. It offers TV output, and will also play MPEG and MP3 files. Requires a card adapter to handle cards other than compact flash. [adorama:ICDGVP60|60gb unit]
[adorama:ICDSDFC|Smartdisk FotoChute, 20 GB "On The Go" Digital Photo Storage with USB Interface] Perhaps the simplest of the lot. You plug this directly to the USB port on your camera, and it transfers to the internal disk. There's no extraneous features like playing MP3 files.
SmartDisk FTX-XT40 FlashTrax XT 40GB Portable Hard Drive & MP3 Player with 3.6" LCD Screen Like the FotoChute above, you connect to the USB port on your camera. This model adds an LCD screen allowing you to view pictures, and you can view them on a TV as well. It plays MP3 files and includes a built in FM radio and allows you to record FM radio broadcasts. What did I say above about extraneous features? [adorama:ICDSDFTX80|80 gb]
[adorama:ICDNVV30|Nixvue Vista NV-030SA Digital Album 30GB Hard Disk with Color LCD viewing Screen] Another unit with an LCD screen. One potentially useful workflow feature is you can do some image manipulations directly with this unit, and you can copy images back to the memory cards. The focus is on features useful to photographers, not general media. [adorama:ICDNVV60|60 gb]
[adorama:ICDND230|Nixvue Digital Album 2, 30GB Portable Hard Drive Disk Storage] A dedicated wallet device. [adorama:ICDND240|40 gb]
[adorama:ICDNDL60|Nixvue Digital Album Light 2, 60GB Portable Hard Drive Disk Storage] This appears to be the same as their "Digital Album 2". The description discusses user interface advances making the device easier to use.
[adorama:ICDPHD20|Argosy Photo HardDisk 20 GB Palm-Sized Portable Backup Storage Device & Card Reader] A dedicated wallet device. Directly supports all card formats requiring no adapters. Can be recharged over the USB bus.
[adorama:ICDEZDM180|EZDigiMagic 20GB Palm-Sized Portable Backup Storage Device] A dedicated wallet device. [adorama:ICDEZDM18040|40 gb]
[adorama:IESP2000|Epson P-2000 Photoviewer, Portable 40GB Multimedia Storage & Viewer with USB 2.0 Interface] A digital wallet offering a large LCD screen on which to view pictures. Prints directly to several EPSON printers. Requires adapters for some card formats. Plays audio and video files. [adorama:IESP4000|80 gb]
[adorama:INKCW|Nikon Coolwalker MSV-01, 30 GB Digital Storage Photo Viewer] Includes an LCD screen allowing you to view the pictures. Can print to any printer supporting PICTBRIDGE. Supports playback to a TV. Requires an adapter for formats other than compact flash.
[adorama:IOMSHD100|Olympus S-HD-100 Photo Life Solutions External 40GB Hard Disk Storage Device with Built-In CPU] A device dedicated to Olympus cameras. It includes a dock into which you insert the camera. It has no user interface of its own, and must depend on the camera to provide that.
[adorama:MMHG120|MediaGear Flash HD to Go Portable 20GB Hard Drive with Flash Memory Slots] A dedicated wallet device. Directly supports all card formats requiring no adapters. [adorama:MMHG140|40 gb] [adorama:MMHG160|60 gb]
iPod with photo adapter: The iPod can be used just as the above devices.
Portable CD or DVD burners: Some digital wallet devices allow you to burn CD or DVD's directly from the memory cards. This should be safer than their hard disk cousins, given that your photos are not stored on a fragile thing that can break if dropped. You do have to be careful about the disk surface, of course.
These devices generally offer incremental additions to a disk. For example if you've shot 100 MB of pictures one day, the device only burns 100 MB of the disk storage. They generally will also span across multiple disks as they're burning data.
[adorama:ICDDBA|Delkin BurnAway Portable 3-in-1 Combo Media Burner, DVD & MP3 Player & Card Reader] offers an interesting combination. Instead of storing the files on a hard disk, it is a CD/DVD burner and you're expected to burn the photos as you go along. You still have to provide power, but that's readily accomplished with power adapters. It also doubles as an MP3 or DVD player.
[adorama:ICDIMP|Jobo Image Maestro Pro, Portable DVD & CD Burner, Burns Directly from Memory Cards] Like the Delkin BurnAway above, burns DVD's or CD's from content on memory cards. Apparently does not require adapters for cards other than compact flash.
[adorama:ICDEZDM220C2|EZDigiMagic 2nd Generation Portable CDR Burner, Combo Digital Photos Backup/Sharing Device, Color Silver/Blue] Reads from any card format without using adapters.
Other portable media device that interfaces with memory cards:
Laptop computer: You really can bring your laptop with you. They aren't that heavy, and what if you want to process your pictures as you go along, or type notes, etc?