You can use quite a variety of card types (SD, SDHC, SDXC, etc.) but cards come in a broad range of quality/reliability and performance differences.
For still photos, the performance differences don't make such a huge difference... but for video its especially imporant to get a good card. I'd get a Class 10 card and if you DO plan to use video then it makes sense to get a particularly good card. The T4i is actually compatible with the new UHS1 standard (UHS = Ultra High Speed) -- these cards have the fastest data-transfer speeds.
SanDisk brand and Lexar brand tend to have the highest quality -- but even these come in a range of performance options and size options.
Whatever you get... get 2. E.g. if you were thinking of getting a single 32GB card it would be better to get two 16GB cards instead. This way you have a spare in case one fails (and occasionally a card will fail). Another reason to own two is ... if you're like me, you'll power up the camera when you are miles from home and see the dreaded "no card" message -- only to realize that this is because your memory card is still in your computer back home. It's nice to have a 2nd card.
Again... if it's just for still shots then almost any speed card will be good enough (it'll just take a little longer to save the images as you shoot). But if shooting video, the card MUST be fast enough to keep up with the frame rate of the video or the buffer will fill up and recording will stop on you all the time.
It's usually a little less than $1 per GB of storage... but the fastest UHS1 class cards are currently more expensive (a SanDisk "Extreme Pro" UHS1 class card -- the fastest and best card they make -- is currently closer to $2 per GB.)
Don't cheap-out too much on the quality of the card... digital camera forums are full of people who post strange camera problems that turn out to be related to problems with the memory card. I'm not saying you should buy the best cards... just stay away from "bargain" cards.
Tim Campbell
5D III, 5D IV, 60Da
