B&H has a solid deal on a two-pack of Sony 16GB Class 10 UHS-1 SDHC cards for $
23.95 [Update: Now $18.95] [Update 2: and they're back to $23.95] (compare the single card price at $23.95). Check it out here at B&H Photo.
Class 10 cards deliver on speed for HD video capture, which goes along with the size advantage of the SDHC spec. You should also check your camera’s specs to make sure it can take advantage of the full speeds available in these cards via the UHS-I standard. For more details on what all the classes and card specs mean, check out my resource article Demystifying SD Cards.