Well I'd be tempted to go with something to complement the rest of your army... so how about a Godhammer Warlord with a pair of Quake Cannons for arms, a carapace landing pad to let you fire the Quake Cannons indirect (and double their range by doing so), and a Vulcan Megabolter for hosing up infantry who get too close.
Though at the moment I'm having fun with a Plasma Lord, with a Plasma Destructor, 2x Plasma Blastguns, and a Quake Cannon.
I like Quake Cannons.

Anyway back to my point, the Godhammer Warlord adds a high volume of ranged MW attacks
and artillery attacks to your army list, both of which you're not particularly flush with.