Yeah, I think hitting the ground running by having some usable Dapps ready is important for the long term process of the project.

I still like the idea of a decentralized email client, if that is at all possible:
https://forum.lisk.io/viewtopic.php?f=8&t=95

And I am a big fan of the dead man switch thingy:
https://forum.lisk.io/viewtopic.php?f=8&t=24

Apart from that, a game always is a good idea. Poker or something along those lines makes sense, obviously, although I am not much of a gambler and don't really like the idea of Lisk being too closely associated with gambling.