I agree with all of the above and below is my standard answer to this question. 1) What type of pictures do you normally take. 2) Are you going to regularly shooting in burst/ high speed continuous , at motorsport or some such thing were speed involved. 3) Is it more important to have pictures to be uploaded to your PC fast over having them saved to the memory card quickly after taking them. 4) Do you shoot in RAW or Jpeg. 5) What is the buffer capability of your camera. ( Important but I wouldn't worry about it) Now what to look out for in the shop: Capacity --- (GB) What is the cards Read speed --- (Mbs) What is the cards Write speed --- (Mbs) You can get cards of all capacities 8, 16, 32 and so on, I prefer to have a few medium capacity rather then one big one because there cheaper to replace if you loss them plus it handy to have spare rather then relying on 1 and when a very large card is wedged full of raw files you will curse yourself. Often card makers market there memory cards with a number displayed in big text on the front of the pack, something like 40Mbs. This number mostly is what is known as the READ speed which means how fast data stored on the card will be downloaded to your PC. Thus the data from our example will be taking from your memory card and put onto your computer at a rate of 40 megabits per second. Write Speed: This is how fast image data can be transferred from your cameras buffer to the memory card the higher this number the faster the camera is ready to take the next shot. Your buffer capacity comes into play here as the card can only save the stuff as quick as the camera makes it. But worst case scenario I rather have a something thats more than capable over cant cope. (Unlike your standard card which deceptively quotes read speed on the front there is normally a ultra or extreme reference made but double check the specs regardless to be sure) This is an example of more than capable/ overkill A memory card with the below specs would be fine for normal use. Price looks like sharp practise but I havent bought one in some time. If it was me the saving on the extreme 32 GB would sway me.