I think it's safe to say they will be around for a while. The only other technology currently used, that I know of, in photography and video are hard drives... and they're losing ground to flash-based media as their capacity increase (you can get a 32Gb SD card for 120$ or so).
Personally, I would not worry about the change in media, just do research on the type of memory card your camera would use (micro-SD, SD, XD, Memory Stick Pro Duo, Compact Flash). For instance, I know that XD cards tend to be more expensive than SD cards, found that out the hard way after buying an Olympus camera.
So do your research but don't worry about flash cards going away anytime in the near future. And even if something new came out, it would be so expensive that it would be impractical for pretty much any customer to buy except for pros.
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Military member by day, amateur photographer by night!
All I need is my car, the open road and my Canon 5D mark II!