The guys from Tom's Hardware did a roundup of 13 SDHC memory cards, you can check it out over here.
The prices of portable memory cards have decreased to almost ridiculous levels: 8 GB SDHC cards now start at only $12. However, enthusiasts don’t want just any memory card—they want one that delivers high write throughput for their devices such as digital cameras, and fast reads, so they can copy contents to their systems quickly. These elite products are much more expensive, so we invited eight popular brands to a shootout.
The reviewers conclude the Lexar Professional series and SanDisk Ultra III cards offer the best performance.