The Wabash and its subsidary roads (Ann Arbor, DT&I, M&LS) used an interesting caboose with a streamlined cupola. The N&W acquired some of these cars when they took over the Wabash. I have heard they painted one in a Bicenntenial scheme. The Burlington had a similiar style caboose as well.
I have always wanted one of these since seeing a real Ann Arbor caboose, but the only commercially O scale model made of these cars was a brass one years ago and it is very hard to find and very expensive.
However, I discovered Mike Packard, who does a custom modification of Lionel steel sided cabooses, and while it's not an exact copy it will certainly do until a RTR model comes along (I'm not holding my breath on that). Mike will do them in the railroad and paint scheme of your choice, and his paintwork is excellent. I had him do one for me in the color scheme of a obscure Upper Peninsula (Mich) railroad that owned one - the Manistique & Lake Superior RR. I was only able to find one color photo of this car but he did a great job of figuring out everything.
The price was really reasonable for the work that he put into it. If anyone is interested in acquiring one of these contact me at my profile address and I'll pass on his info.
Here's a cell phone picture of an Ann Arbor car that he did. Sorry for the poor quality!
John