I think of cards as the cheap bit, consumable almost, especially when compared to the amount of money tied up in the rest your equipment, it's much like film used to be.
That's without putting any value on your images, either in terms of real money or sentimental value.
I would recommend buying a good brand of card from a reputable source or outlet, as there are a fair few fakes kicking about on the Internet.
For me, my images are my next meal, hence I use what I consider to be the best and in my case that's SanDisk Extreme. I've never had a problem or been let down under any conditions, but that having been said I still change 'em for new ones very couple of months.