this advent calendar caught my eye - It's easy to make and would be major fun for the kids (each tin has a surprise of your choice inside). I found it HERE. It's not nativity-esque, but it could be put together in one or two afternoons!
eventually of course, I'll have to actually make some of these things myself... not sure when that's going to happen since I've just decided to do NaNoWriMo again this year!
Here's another one, for the sewing-crafty types. There are no instructions (it was made to sell) but I found it HERE, and it's a lovely idea.