The SanDisk Extreme III series is more geared toward "high-end" D-SLR cameras with higher write speeds. SanDisk also has the Ultra II series, which is rated at 15MB/s and costs a little less. I use SanDisk Ultra II Compact Flash cards with my D-SLR, but it is older and wouldn't be able to take advantage of the Extreme III speed.
Tom's did a review on SDHC memory cards that should be helpful. Here is the
link. Looks like the regular PNY Optima SDHC cards outperformed their Optima Pro series cards. I think the PNY cards would be good.