Buy the card locally from a bricks and mortar store if you want to be sure its decent.
I swear a good % of the ones sold online really cheap are fakes (from the official factories, cards that did not make the grade, packaged and sold anyway by dodgy people).
I've had no issues with my locally purchased 8GB Class 4 sandisk.
A 4GB kingston I purchased from DX was laggy as hell until formatted with the panasonic formatter. The MicroSD to SD adapter did not work also.
I guess when you save some $ online you are choosing to 'take the risk'.