The Acekard 2i is claimed to be the world's first fully-working DSi flash cartridge with cart mavens Acekard claiming the device supports all of the DSi's new features - including the ability to read and store data on MicroSD cards in the new slot.
This video shows what appears to be the menu system (curiously, the site says "The Acekard R.P.G. utilizes the idea of the iPhone which gives the customer a totally new control experience." which I think is just a fancy way of saying that the menu can use the touchscreen) with a quick segue into a probably not-that-legal version of Castlevania. Never mind, Nintendo. You had a good run at being piracy free for, what, two months?
Acekard2i For DSi Released! [Acekard - thanks to Wraggster for the tip]