How to Choose the Right Memory Card
Most digital cameras use an SD (Secure Digital) card to store images, so at some point, you'll need to buy one. While there are many cards in the market today, make sure you get one that meets your needs.
How much space do you need? The standard SD card has a storage capacity of up to 2GB while the High Capacity (SDHC) format supports up to 32GB of data. The new Extended Capacity (SDXC) memory card supports up to 2TB of data, but you'll need a new camera that supports that latest format.
Compatibility and Speed
While most digital cameras are compatible with most SD cards, it is important to find out from your camera's manufacturer (or by consulting your camera's manual) what type of card is compatible with your camera, particularly if you're buying a high-speed card. SD cards come in speed classes 2, 4, 6, and 10, which mean that they write data at 2MB per second, 4MB per second, and so on. A 6X card should meet and even exceed the needs of most casual photographers.
Data Safety Considerations
For most people, a higher capacity SD card will always be preferable to a lower capacity one, but then you may be putting all your proverbial eggs in one basket. Buying several smaller cards will protect against losing all your images should one become corrupted. Better yet, download your images often and back them up.
You'll also want at least an 8GB card if you are shooting in the RAW image format or if you shoot video. This handy chart compiled by the SD Association lets you see how much video, photography, and music you can load onto different sizes of SD cards. A 4GB card, for example, holds 40 minutes of high-quality video, 1540 photos, and 68 hours of music.