Digital Camera Memory

CompactFlash is one of the most common types of digital camera memory. Most high-end digital cameras, and all digital SLRs are CompactFlash compatible.
There are two physical sizes of CompactFlash - Type I and Type II. Type II is thicker and some cameras will only accept Type I CompactFlash. Type II CompactFlash is usually higher capacity. The most common Type II CompactFlash cards are mechanical, MicroDrive, memory cards.
The main benefit of CompactFlash, besides availability, is that it has a controller chip in the card. The controller chip allows higher transfer rates. Most cameras can't take advantage of this extra speed, though. Only cameras with larger internal buffers - mostly digital SLRs - can take advantage of high-speed CompactFlash.
CompactFlash is inexpensive, easy to find, and works in a lot of digital cameras. For those reasons, it's one of the most desirable types of digital camera memory.

Secure Digital & MultiMedia Cards

The smallest available memory cards, Secure Digital and MultiMediaCard memory allow for very small cameras and can also be used in selected PDAs, organizers, phones, and MP3 players. The current maximum capacity for Secure Digital and MultiMediaCard cards is 512 MB.
The only difference between the two memory types is that Secure Digital cards have a write-protect switch for added data security.

Introduced by Olympus and Fuji in 2002, the xD Picture card is the newest digital camera memory format. Its tiny size - 0.97" x 0.98" x 0.67" - means it can be used in very small cameras. The xD Picture Card can also be used in any CompactFlash compatible camera with the available CompactFlash adapter. It's currently available in capacities up to 512 MB, with larger capacity cards to be available soon.
Since it was developed and introduced by Olymous and Fuji, most current compact digital cameras from those manufacturers use the xD Picture Card media.

Memory Stick was developed by Sony for their CyberShot digital cameras and other Sony electronic devices. With the exception of a very few cameras, Memory Stick is only compatible with Sony digital cameras. That means if you have Memory Stick media for a camera and you decide to buy another brand of camera, the Memory Stick cards you own are not likely to work with the new camera. On the other hand, if you own other Sony devices, there might be benefits to owning Memory Stick. Sony MP3 players, PDA's and selected Sony Vaio computers also accept Memory Stick media.

MicroDrive

The MicroDrive card is actually a miniature hard drive housed in a Type II CompactFlash chassis. The IBM MicroDrive was the first compact memory card to offer a full 1 Gigabyte storage capacity. Although flash memory has bypassed the MicroDrive in capacity, the MicroDrive is still the best buy on a dollar-per-byte basis.
MicroDrives have a reputation for being delicate and unreliable. They are more prone to failure since they have moving parts that can wear, or be damaged. But when handled normally and not abused, they are very reliable. Because of their moving parts, MicroDrives use more battery power than flash memory. And compared to new, high-speed CompactFlash cards, MicroDrive seek and write times are fairly slow. But if you need Gigs of cheap digital camera memory, MicroDrives are still the most bang-for-the-buck.

SmartMedia

SmartMedia used to be one of the most common types of digital camera storage media. It was used in most Olympus and Fuji digital cameras until the introduction the xD Picture card, in 2002. SmartMedia is being pahased out for newer memory types, but it should be available for quite some time, still. And since it's being phased out, it's become very inexpensive. If you buy a camera that uses SmartMedia it might be a good idea to stock up on memory cards, though. They might not be available for too much longer. SmartMedia is available in capacities up to 128 megabytes.

Card Readers

Card readers are the most efficient way to download your digital digital memory cards and a highly recommended digital camera accessory. Card readers plug into your computer via USB or FireWire port and allow you to transfer your files without using your camera's batteries or dealing with cables. You install the card reader as you would any other USB or FireWire device and plug the card into the reader when you want to transfer your images. The memory card will show up on your computer as a separate, removable drive when it's plugged into the reader.
Card readers are available in internal and external models with USB, USB 2.0, and FireWire connections. USB 2.0 and FireWire readers have considerably faster transfer rates than most cameras - another good reason to use a card reader instead of using your camera's supplied USB connection.