Check out Trek's Soho Coffee Mug. Its designed to fit into bottle cages and is also insulated.

Plus its on sale right now for Christmas at the shop I work at. It might also be at your local Trek Partner Dealership. (Check the Trek website for a concept store in your area.)

Im not a coffee drinker but I know of people that use it and they are liking it.

*edit* found the item on Trek's website. http://store.trekbikes.com/jump.jsp?...&bShopOnline=1