Ok, well, I'm also doing my own wedding cake! Are we all nuts?
You can bake them all about 2 months ahead of time and freeze them, but don't pre-frost them. You can fill them first if you want, though, but do NOT freeze fondant.
I saw a couple of you saying you're just using a box mix and I wanted to suggest that you try using milk instead of the water for what you add to the box stuff, and use butter instead of oil. This makes it soooo much richer! Also, if it's a chocolate cake, use sourcream or buttermilk instead of the water and also use butter, not oil. You can use milk instead of water in almost any cake mix for better results. I've been experimenting with recipes and just got the "Cake Mix Doctor" book that tells a ton of recipes you can make starting with a box cake. I love the Bride's White Cake - which was just a white cake with milk instead of water and butter instead of oil and a little extra vanilla extract. Amazing! The "Better Than Sex Chocolate" cake came out a bit dry after two days out and iced, so I don't think I'll use that one. I have yet to try the buttermilk in the chocolate mix, though.
Note to GreenCarGirl - Make sure you give the groomsmen a diagram on how to do it, and give at least one a lesson on how to assemble it with the dowels and plates, if you're doing a stacked or tiered cake. It's not really something you can figure out on the fly too easily..
Best of luck, everyone!