So like most people when they bought their new camera you have to choose a good SD Card that is a decent size and fast. Well if you go to your normal walmart or other tech like stores you'll most likely end up picking up the first thing you see or possibly they will have a extreme card and you think great that's the one I need. What you should always pay attention too is the card actually compatible with your camera? Just because it's on sale doesn't mean that its a good fit, yes it will work but you may experience the wright light is always on and you only are able to snap a few pictures then you have to wait, and wait and wait. I myself did this same thing and got frustrated so I dumped my older cards and went for a 45mb/s sanddisk extreme sd card which has suited me so far but I still have that issue with the wait if I take a lot of pictures in rapid succession. The next card I plan on getting and you should get one too is the Sandisk Extreme Pro cards. They are sold in various sizes and have a great wright speed a must have for anyone with a newer DSLR.
You can also get the Compact Flash version of these cards that have a 5mb/s higher write speed.