I guess throwing rocks is the big thing, but it's a little bit... inelegant. For starters it's not very precise and you end up wasting a lot of 'innocent' people without necessarily hitting strategic targets. If you're just after a lot of carnage then I guess that's OK.
The main advantage that the Moon has in this war is the small gravity well. You can get off the Moon a lot easier, and that means you can put much more massive objects into Earth orbit than Earth can. You also don't have to worry about atmospheric pollutants from your rocket exhaust or atmospheric drag, which is nice. And no atmosphere also means you don't have to worry about streamlining your designs.
So what else could we launch from Luna that would be better than rocks?
How about dozens or hundreds of Kinetic Bombardment platforms?
These things are nasty. Take a bunch of tungsten rods, say a hundred kilograms or so each. Load them into firing tubes with carefully calibrated charges to allow you to deorbit them onto a ground target. Put say 50 of them into a smallish satellite and launch it into orbit. Repeat as many times as you like.
The beauty of these little Rods from God is that they hit the ground like tactical nukes, with none of the radiation effects. Aiming is a bit of a problem, what with the messy atmosphere to go through, but when you're firing 10 or 50 of these things into a very small area you can adjust pretty well. And the area is small. These things are tactical as hell, the only thing stopping them from being surgical is the atmosphere being unpredictable.
RfG bombardment could be targeted on very small areas. Like launch facilities. Deny space to your opponents and they're out of the war.
But that's not the worst thing you can do with these nasty little buggers. What happens when you fire all of your RfG payload into LEO and let them orbit? You end up with Kessler Syndrome's big brother. Not only do you scrub LEO free of any functioning satellite system, you have effective screened off the Earth from space. You can't go there, but they can't come out to hurt you anymore. 50,000 or so scattered in various orbits around the Earth would be enough I think.
Of course they aren't going to stay up there forever. Eventually orbital decay is going to bring them down, and there's no way to figure out where. And once they're all down there's not going to be much left of the surface. Perhaps this isn't the nicest approach?
But since we're throwing 'nice' out the window anyway - we're at war, after all, so we can apparently justify any atrocity - why not make a few thousand concrete bombs and use them to wipe out all the military assets you can reach. They're little more than the rocks everyone else wants to throw, but they are steerable so you're more likely to get the target you wanted. Deorbit into the general area, then steer down to the target. Kinetic bombardment with increased accuracy. And you can make them as big as you like, so taking out entire cities... um, I mean military bases will be easy.