Memory Card Speed
Memory cards come in many different speeds ranging from 8x to 133x. The prices generally go up in line with the speed increases. The speed of the memory card affects how fast your camera will be able to write the photo to the memory card. A faster memory card means that you can take photos faster. The more megapixels your camera is, the larger the file is that needs to be written, therefore you'll want to get a faster card. Here is a chart of the different speeds and their approximate MB per second.
8X = 1.2 Mb/sec
12X = 1.8 Mb/sec
20X = 3.0 Mb/sec
25X = 3.8 Mb/sec
30X = 4.5 Mb/sec
40X = 6.0 Mb/sec
60X = 9.0 Mb/sec
66X = 10.0 Mb/sec
80X = 12.0 Mb/sec
90X = 15.0 Mb/sec
133X = 20.0 Mb/sec
The lower end of the scale is more for older cameras with a lower pixel count. If you have a 3 megapixel camera then you sould be fine with a 12x or 30x. If you have a 7 megapixel camera, you'll want something in the mid-range around 40x. If you have a digital SLR, you'll want to get the fastest memory card you can so that you can quickly take multiple images in quick succession.