Stick with well-known brands like Sandisk, Samsung, Toshiba, or Sony. Class 10 is common--don't get anything slower than that. Make sure you buy from a reputable seller, and not from a random seller on eBay (which would increase your risk for counterfeits). Get as large of a card as you can afford, but be aware that the really big cards sometimes seem to have more problems (like the 128 GB size).