I think you're more worried about it than most of us are. If you're just giving general wishes like on your LJ or something, there's nothing wrong with "merry christmas". People who celebrate it will be happy and those of us who don't know it's not aimed at us anyway. Personally I'd prefer that to the generally happy day thing because it's not like you're going to wish people a generally happy day every day. It feels like it's being way too self-conscious about the whole thing. Like "well I want to wish people merry christmas but gee I don't want those people who don't celebrate it to feel left out so I'd better include them somehow". If we don't observe christmas then we're already "left out" of everything christmas-related and it doesn't bother us. Not our festival. If you want to wish people who celebrate it merry christmas then go ahead, it's got nothing to do with us. There's no need to wish us anything except happy new year or whatever.

That said, it's still not a big deal and not really worth worrying about. Everyone I know who doesn't celebrate christmas takes any kind of well-wish in the spirit that it's meant. The only one that does bug me is the combined one you mentioned because AFAIK (bad jew alert) channukah is already over, so there's no point in wishing me a happy one. It just shows people want to be inclusive without actually bothering to find out anything about what they're trying to include. Also yeah, it's not even nearly an equivalent. The best equivalent in my family at least is pesach and even that doesn't involve presents.