I know you can't tell us areas and realms you've got planned, I want to be surprised too! But it does hinder our helping out with brainstorming ideas.
Anyway, I just thought I'd throw something out there and see if it sticks... ;)
A Fae realm. What Dresden calls the NeverNever. Tied to our seasons, each kingdom would be in ascendance at different times of the year. This would give you the excuse of visiting a winter wonderland during the holiday season as the Winter Queen relaxes her attitudes towards mortals! (and maybe earn some brownie points with her!) Har !
Other times might be good for a "storybook" mission or two. Really put the grim back into Grimm's Faery Tales! ;)
Alien worlds. Perhaps in one issue we can be called upon to help out a peaceful alien culture in the midst of an invasion. We could go by portal instead of actual spaceflight. (though I'd love that!)
Alien invasion. Something a little different. How about Cthulhu-esque type aliens (small!) in a future Issue; the aforementioned invaders from the other world, having learned of us now. There could be a huge organic mothership that would be a realm in and of itself when we take the fight to them.
Can't think of any others right now. :)
"Listen, and understand. City of Titans is out there. It can't be bargained with. It can't be reasoned with. It doesn't feel pity, or remorse, or fear. And it absolutely will not stop, ever, until we are live!"