The more dense the cake is the easier it is to carve... pound cake for example, or the durable cake recipe.
http://www.cakecentral.com/cake_recipe-1972-Durable-Cake-for-3D-and-Wedding-Cakes.html
Freezing definitely helps. Also, if it is an area that just won't hold up to carving, you might try using rice crispy treats.
HTH 
Well, all of your ideas were very helpful. I used the 3D/Durable cake receipe and I froze the cake. My husband actually carved the cake for me. He said is a great idea to freeze if first. The frame of the bike was yellow and the wheels were chocolate. They loved the cake and also said that it was delicious! I would have loved to smooth it out more, but it was 1 AM when I started to clean up and I had to be up at 5:30 AM to get to Orlando.
Thank you so much for all your help!
Wow, that looks like a carve that definitely required a plan. 
Great idea, and a very nicely done! 
I have been there with the late night/early morning finishes. I don't imagine there are too many of us that haven't. It's times like these when it's nice to have a few tricks to help things move along as quickly and easily as possible. I don't know if you've seen this article, but the next time you find yourself there and you want to smooth you might try the Viva Method. It's quick and easy, and a good tip to know especially in the wee hours of the morning.
Oh boy, I have been looking around and all I can find is this one,
http://www.parents.com/parents/story.jhtml?storyid=/templatedata/parents/story/data/4214.xml&catref=prt72
Maybe you could doctor it a bit to make it look more realistic.
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