The best memory cards are Sandisk Extreme 3 and 4 or Lexar.
The reason I say this is they have the ability to repair themselves and they are fast.
All memory card start life as 64Gb chips these are tested to find how many good sectors they have and how fast they can reliably work.
Top quality ones go to the Military at extravagant prices the lesser ones are packaged and labeled with the size and speed they can reliably accomplish.
This means that on every card less than 64Gb there are free good pages of memory space available.
Extreme 3 cards hold their root directory (which keeps tabs on the start and end address of every file) in a re-programmable chip, so should any page of memory corrupt the chip can automatically program this chip to allocate some of the spare memory page(s), so you never loose a file.
Add to this in the retail packs you get Rescue Pro software which can get pictures off a card should you accidentally format it, and a nice carry case they're a bargain. Extreme 4 cards come with a very fast reader as there are not many readers that can keep up with them.
A point to note is that a 2Gb SD Extreme 3 card is (marginally) faster than any SDHC card due to the way they work.
Chris