A quick thought for some sites on the Lower Planes. Evil gods need worship just as much as good gods -- and they almost certainly don't get it from most races. (They seem to be as powerful or nearly as powerful, though perhaps this is the result of additional power inputs from sacrificial rituals rather than the "willing sacrifice" of believers' worship energies.) However, in a modern setting where information flows rapidly, people can see the planes that the evil powers govern, and this might begin cutting off the supply of worship and sacrifices that they *were* getting. As information technology advances, propaganda techniques would follow suit, don't you think? Consider the following proposals:
(1) The areas around the most commonly-trafficked gates to Lower Planes are carefully controlled "port towns" beyond which few bashers are let through. The demons staffing the place and trading with outsiders are the smoothest, prettiest ones they've got (doubtless heavily sprinkled with erinyes and succubi).
(2) The inhabitants of the Lower Planes use these areas to promote philosophies that would encourage willing worship of evil gods. In particular they would promulgate the notion that evil is in the eye of the beholder. "Yeah, berk, I know what a 'Detect Evil' spell looks like. Have you ever stopped to ask yourself just what that spell's detecting? Maybe it's 'Detect Enemies of My God.' Or maybe it's just 'Detect Berks What The Wizard That Researched This Spell Didn't Like.' Ever think of that?"
Each plane's typical inhabitants would, of course, have particular philosophies in their 'port towns.'
CARCERI: A curiously inside-out town fills the inside of square walls whose battlements look *in*; the idea is that the rest of the plane is a prison, and this tiny space is the "outside".
Propaganda: We get a bad rap, you know. Sure, they call us demons and we look a sight, but that's just the way we have to be to do our jobs. We're really performing a great service for the whole multiverse -- we're keeping the most dangerous creatures in existence locked away for your protection! Care to help us out?
Town staff: Best if you don't go past the walls of the city, lad. That's where the prisoners are. *Really* best if you don't go outside without proper ID. Then we couldn't tell you weren't a prisoner yourself, get my drift?
ACHERON: Troops from all the wandering armies march the streets, kept in line by strict and vicious punishments for breaking the DMZ agreement.
Propaganda: It's a *war* out there, berk! The whole Great Ring is battle, pure and simple, and we intend to win it. Now if that's too sodding *tough* for you, go back to Sigil and wait for the victors to come claim you. If you're interested in showing you're a man and signing up with the winners, we're recruiting.
Town Staff: See here. You're a civilian and this is a military outpost. Go outside authorized areas and you'll be shot on sight, it's as simple as that.
BAATOR: The city on Avernus is clean and neat; minor demons under strict orders not to talk to the tourists scurry around making sure it stays that way. It has a harsh stone-and-steel industrial aesthetic that would put Soveit architecture to shame. It fills the top of a plateau that towers hundreds of feet over the plain via a sheer drop, the roads down narrow and carefully controlled. Malsheem, Dis, Jangling Hiter, and the other cities below have their own styles but similarly controlled trade quarters.
Propaganda: Baator welcomes entrepreneurs capable of competing in the modern multiverse. Our numerous cities are the perfect place for you to do business; we uniquely combine the benefits of well-organized infrastructure and the stable legal environment so necessary for modern industry, with a laissez-faire philosophy of letting you run whatever business you choose, regardless of its nature, that you will never find on the Upper Planes. We firmly believe that government has no place legislating morality.
Town Staff: Sir, you'll need authorization to exit through here. No sir, I believe the emigrant quota has been filled for today. You'll have to talk to my superiors, sir.
Haven't come up with ideas for the others presently, though for Pandemonium the line "have you *seen* Mechanus? The unending, pitiless machine? *That*'s hell, berk!" seems to be floating around my head. It would certainly confuse the issue of what evil actually is a little more.