Datel launched a 2GB (40 USD) and 4GB (50 USD) Memory Card compatible with the Xbox360. It even includes a Micro SD slot for more memory (up to 16GB). Afaik this is the first unofficial memory card for the Xbox360 (unlike normal USB memory sticks/hdds these can be used as real memory card to store gamesaves and XBL content). Looks like Datel managed to bypass/hack the protection Microsoft uses on their memcards.
From - http://www.xbox-scene.com/