This is an interesting question, I'm pondering on this for quite some time. With the recent release of Age of Empires: Mythologies i think the total has come to 4 or so. (Please correct me if i'm mistaken) I know this is not a large number, this might be a coincidence for all i know but do you think we will see more and more of this as the DS and the DSI come along?

So far these are the games I know of:

1.Age of Empires: Age of Kings(I think)
2.Age of Empires: Mythologies
3.Syberia
4.Populus DS