basically you are looking at the Class rating on SD cards. The higher the class rating, the faster the memory is, and more suitable for higher bandwidth (Megabytes per second) applications. I believe a Class 6 SD card is suitable for HD full motion video transfer with no lag. SDHC Ultra - Class 2 - 2 MB/sec SDHC Ultra II - Class 4 - 4 MB/sec SDHC Ultra III - Class 6 - 6 MB/sec I've purchased only Class 6 cards recently for my nikons. YOu can get good deals, but you should be fine with Ultra II.