Coal mining/refining in an AFK sense is pretty sweet too, if you can rig it properly, and you don't get molested. Not really a combo, but eh. There isn't a lot of combo actions in this game, seemingly. Though going one of the high-trade governments, setting up tons of trades, then switching works too.
I'm finding after sticking it out for a while that I rather like terraforming to URO and then building a reactor. You don't have to worry about keeping coal around except for fighting and occasionally trading for a few to build/scrap. Then you combine that with Lazzez-Faire industry because what the hell, you've already got a -10 GM penalty from radioactivity in the first place. LF gives you a +1 PM bonus per Power, so you build a bunch of Power-consuming buildings and get bonus URO for it which makes up for the fact that you spend your URO to power your Power. You have EUR around all the time, which makes people not want to mess with you in combat, because they know you're going to f*** them up on the countershot, especially if you have a few+ cannons sitting around.
I've settled into a nice little groove with a 10 PM so I get double URO consistently, and my negative GM is ignored by my little greenhouse. Sure, my city is packed nearly solid and I'm gonna get raped when someone finally decides to be stupid and attack me, but when they do, they're gonna take 4 EUR shots up the butt in reply, so they'd better count on losing a lot of buildings when they make that decision.