This is the exact point where a digital camera begins to pay for itself, especially if you're an avid photographer. If you're shooting on film, every time you shoot, you need to buy the film and pay for the developing. After a while, it adds up. For me, a typical shoot often costs well in excess of $200-$300. Of course, I shoot a lot of film.
By contrast, as long as you've got a big enough memory card, or a few, there's no incremental cost each time you shoot your pictures on a digital camera. You shoot, using up the card. You upload the pictures to your computer. You then erase and reuse the card. There's no cash outlay.
Frankly, I've long been amazed that this hasn't been a heavily promoted selling point by the manufacturers. It's a real, honest-to-goodness, bona-fide benefit.
The memory card formats
There are a bunch of image storage formats in digital cameras. Three of the most popular are Secure Digital (SD), CompactFlash, and SmartMedia. Sony also offers the Memory Stick format, but that pretty-much runs only on Sony devices, so it's less of a standard and more of their proprietary game.
This is important, because memory cards don't just work in cameras. In fact, all three of the formats I'm discussing in this article work in PDAs and MP3 players as well as in cameras. And, some of them work in other devices; in fact the SD Card Association (the trade group for the SD format) claim that SD cards will even store recipes for microwave ovens!
In some cases, the data on the cards is interchangeable from device type to device type, but that's rare. What's more common though, is if you buy a bunch of cards of one type, you can use them across a range of your consumer electronics.
For example, I've got both an HP Jornada (a Pocket PC) and a digital camera, both of which use the CompactFlash format. Sometimes, I'll use my 128MB CompactFlash card to hold music and software for my Pocket PC. Other times, like if I'm going out to take some snapshots, I'll clear off the card and stick it into my camera.
So, one criteria for choosing the format of the card is whether or not you've got other devices using the same format. Most PDAs (including Palm) seem to be moving to SD format, so if you're going to be using a Palm PDA, you may want to consider finding a camera that also uses SD.
There are electrical and performance differences in the formats, but from a consumer perspective, those differences don't matter. They all function quite nicely. Personally, I'm a tad bit less comfortable with SD because the format is supposed to incorporate some form of digital rights management, but I've yet to see that "feature" (a feature designed to hamper our use of the technology, not add to consumer enjoyment) incorporated in cameras or PDAs, so at this time there's no good reason for me to advise against it.
Another criteria for choosing one format over the other might be price. In reality, though, there's a great deal of price parity across all the formats (although, given that Memory Stick is a Sony proprietary format, it tends to be a bit more costly).