Amoebattle is a simple RTS in which you control a group of amoebas in a microscopic campaign. Originally designed as a DS game, the iPhone version made it to market first -- it's available from the App Store today for $5. The DSiWare version has been approved by Nintendo and will be released soon, though there's no specific date yet.
Intrinsic seems to be developing "iOS/DSiWare" into a full-on business model; a previous App Store release, Penguin Patrol, is due for release on DSiWare tomorrow. All are published by Grab Games, who recently acquired Intrinsic.