Emblem of fire
Don't forget that GBA slot -- it expands your DS library to insane proportions! Of course, if you're an Advance Wars fan, you've probably also played through all the Fire Emblem games you can get your hands on, but just in case you haven't, we wanted to point out the GBA entries in the franchise. Like Advance Wars, Fire Emblem is made by Intelligent Systems, and the two franchises enjoy a lot of similarities, and also like Advance Wars, Fire Emblem games are often well-received and highly rated. If you haven't played the GBA games, you're really missing out.
Of course, there's also a Fire Emblem DS on the way....