I've always purchased my cards from a source that I easily could return them to, if necessary--too many fake cards around (so sad to hear!) and even fine cards can have physical defects. Generally, from a large local electronics store, Fry's Electronics (which also sells online at frys.com, with only $1.99 for the shipping of cards) when the cards are on super-special pricing, bringing the price down to earth (even though a rebate might be needed).
I prefer SanDisk cards--they just seem to work, and faster than the card rating would indicate. Not typically on sale, though, and so I've also ended up with Kingston (not the fastest, but at the rated class and fine for a music player), A-Data and Patriot cards, none of which has had a counterfeit or defect issue.