I am not a commuter, nor am I a coffee drinker. However, I know of a great product for coffee drinking commuters—the Trek Soho Commuter Mug. This 18-ounce coffee mug has a stainless steel exterior with a plastic interior, and is designed to fit in the water bottle cage on your bike. The insulation in the mug is decent, but the one weak spot is the lid—it is thin so there is going to be some heat less here.
Even though I am not a coffee drinker I have used this mug on occasions—it keeps my Gatorade or other sports drink from freezing in the winter. I know this is not the intended use, but winter cycling forces all of us to make compromises. The only downside of this mug is the height—it is nine inches tall and this might be a problem for small framed bikes. However, if you use the Zefal WIIZ Side Mount Bicycle Water Bottle Cage it should fit without any problem.
If you are looking for the right coffee to put in this mug you might want to try the new Sip, Clip and Go! Coffee that my friend Anna reviewed on this blog a few months ago.
The Trek Soho Commuter Mug retails for $15. The local bike shop I use just a got a new shipment of these mugs in, but I noticed yesterday that they are out of stock at the Trek online store (Item #05650). If you cannot find this mug at you local shop you might want to check out the 16-ounce Travel Mug from Sip, Clip and Go! Coffee (I have not tested this mug myself, but it looks like something that would work well for any commuter).