Stay away from the ones on EBAY! They're 2 gig cards formatted to show 4. But if you're lucky enough to get it to work - then you'll run into a wall when you hit the 2 gig mark. The card will be unable to take more data - even if you hook it up directly to a computer.

I learned this from various reviews on this site - there's a huge thread listing values in SD cards, I'd suggest looking for that.