I recently received the Eco Cup mug from DCI. Unlike the similar I Am Not A Paper Cup mug by the same company, the Eco Mug is single walled (no insulation) and holds 16 ounces instead of 10. Since it's solid porcelain, the Eco Cup comes with a silicone sleeve to keep from burning your hands - the mug gets hot, especially if you put it in the microwave. The sleeve does a fine job of protecting your digits. Overall I think the capacity of the Eco Cup makes it superior to the I Am Not A Paper Cup.
I bought this mug because the vast majority of travel mugs on the market are made of plastic or metal, and I haven't had good luck putting either of those in the microwave. I like my coffee hot, so by the time I drive to work, I'm ready to zap it for 30 seconds and bring it back up to operating temperature. The Eco Cup lets me do that. I've had several co-workers confuse the Eco Cup for a Starbucks paper cup until I thunked it on their desks - even empty, it's heavy.
Downsides: The white silicone lid can pick up coffee stains over time. You're not supposed to put the lid through the dishwasher, rather, you soak it in boiling water with lemon. That works okay but doesn't quite get all the coffee color out. The mug's capacity is listed at 16 ounces (in reality it holds closer to 14 unless you fill it to the brim) which is a decent amount but I wish it were a little larger. The mug is not insulated, so it won't keep your drink as hot for as long as a thermos if you're traveling away from civilization. However, since there's no metal or plastic in the mug, you can easily microwave it once you get to the office. The lid is not airtight so if it tips over, it will spill.
I like the Eco Mug and would recommend it to anyone who wants to be able to get their coffee extra hot in the microwave. Be careful to buy the mug made by DCI, and not one of the cheaper knockoffs that Amazon also sells.
Photo: Nikon D90 with 17-55mm f/2.8