Obliterators are a solid choice. As Iron Warriors they get tank/building hunters to add to their invaluable array of weapons. You can not go wrong with these guys except knowing when to deepstrike them and when to deploy them normally.
With the Dark Vengeance set you could legitimately build a CAD with Chaos Lord and Obliterators filling you mandatory requirements. Then attach a Helcult Formation Detachment using the Helbrute and Cultists. That would give you a solid, battle-forged army with the stuff you've already got and you can add more of the fun, killy stuff to the CAD as you expand your model collection.
Helldrakes are pretty awesome, though not as powerful as they used to be. I'm meh on bikers but I've not really played them enough to fairly judge them.