Here's my standard advice. Sure, buy a decent brand from a reputable dealer, but don't leave it there. I've bought mostly cheap cards from Amazon and Newegg (a lot of Transcend). But I always test them thoroughly before I use them for anything important.
The easiest way to test a new flash card is using a disk wipe program, such as DBAN. You make bootable media (CD or flash drive) and it wipes attached drives by overwriting several times. I typically do a 20-pass operation on each new card. If the card is good after 20-passes, it'll probably be good in the field (assuming you treat it with reasonable care).
CAUTION!!!: It's best to do this on a machine without a hard drive so you don't accidentally wipe your computer down to entropy.