I've bought generic brand SD cards from 7DayShop and never had problems. These are largely commodity items at this stage and ultimately house the same flash memory chips from a handful of chip manufacturers (e.g. Samsung, Toshiba etc.). Construction quality may vary but I doubt that much. One thing to bear in mind is the relative speed of different cards and it's not always easy to determine what this is and what your device (e.g. camera) is capable of. Also - don't bother with higher capacity SD cards if your device will not benefit from them (e.g. some (older?) cameras will only use 1GB of an SD card no matter what the total capacity is. Oh - and, as ever, backup regularly!