There's Ninjatown, Plants vs. Zombies, and Fieldrunners (DSiWare). I've downloaded the last one, but have never actually played it.
Just recently, I beat Plants vs. Zombies on the PC and have been helping a seven-year old with it on the DS. After beating Ninjatown months ago, I'd say it's far better than Plants vs. Zombies. Definitely longer w/ more levels! I would suggest going with Ninjatown over any of the others.