Why not put a few ads on the forum if you're viewing it as a guest? There's more guests then there are users online, and I think most of them view the forums and such. Such as other forumsites, they have ads if you're a guest, and it says "Login to remove these ads" etc.
I've actually thought of this before, it seems like a good idea, but as Seph and Loony have said, it will probably make people not like RomUlation and thats not good. But I guess it's fair since registration is free anyway.
Well, you can't really do anything on RomUlation if you're a guest, good idea if in need of money though.