I'm toying with the idea of a Chaos Daemon army as I'm really fond of the models of the upcoming Daemon wave. It would be a combined Slaanesh and Tzeentch army, I always loved Slaanesh and I like the direction of the plastic Daemonettes.
I imagine there would be a lot of Daemonettes and Seekers, backed up by some Pink Horrors, a Tzeentch themed Soul Grinder, a choppy Slaanesh Daemon Prince with Iron Hide and a shooty Tzeentch Prince with wings. Maybe even Fateweaver, as it is the only Greater Daemon that doesn't make your eyes sore.
I also thought it would be cool to use some CSM Possesed models as substitutes for Fiends, as the models are both expensive and crappy (seriously, why do they still let Trish Carden/Morrison sculpt things?). Visually they would also create a link to the Slaanesh Daemon Prince (I'd use the torso with the power armour fragments here) and to the armour of the Soul Grinder. I always thought Soul Grinder with his armoured Defiler parts to stand out between the other more "Fantasy" looking Daemons. I hope that they will add some more Daemon Engines in the next edition of the codex, Forgeworld has already done some interesting stuff.
Off course all of this is far away because I've got so many unpainted stuff and a Skaven army to do first!