About dealextreme: buying from that site is pretty much a hit-and-miss. I have actually bought a lot of stuff from there. They're cheap, but also terribly slow at shipping. They also don't usually have goods in stock, and they backorder from the suppliers. NEVER buy there if you are in hurry, never.
Especially about memory cards, you never know if you're gonna get a genuine or a fake item. They just seem to ship whatever they have in stock. You might be lucky or not
Just buy from Amazon if you can. I have bought a Samsung 16GB class 10 for my Desire Z for 20€, and the increase in speed while loading the gallery is noticeable.