Secure Digital High Capacity or SDHC cards have just hit the market, breaking the 2GB size barrier previously in place. These new cards have very limited backwards compatibility, but newer devices are beginning to adopt the new standard quickly.
As file sizes get bigger, the speed of cards becomes an issue, limiting the amount of continuous video you can record as well as the amount of sequential shots in a row you can take. Gizmodo has a great comparison and test of nine of the major brands of SDHC card in two major classes of speed, 4 mbs and 6 mbs.
In the “Class 4” category the Sandisk Ultra II took top honors and the Lexar 133x Pro SD card took tops in the “Class 6” category. Lexar’s cards make a great secondary card for the 1D Mark III or primary for the Canon TX1’s HD quality video recording.