I am fortunate enough to have a coffee shop a block from my house that uses real mugs. The one a little further away in my neighborhood does not, however, nor does the landfill nightmare known as Starbucks. Plus if you're grabbing a coffee to go, you're stuck with a throwaway cup unless you've worked out a deal to fill up your own.
I always say that if every person changed a few insignificant regular habits, they could reduce their impact on the planet far more than by doing more hyped actions such as buying carbon offsets for a flight. Here's one that's dead easy: buy one of these cool Cupcoats to put around your take-out coffee instead of slapping on the cardboard sleeve you see everyone using. If you only buy one cup of coffee a week, that's 52 pieces of garbage avoided. If you pick up a cup every day---whoa Nellie! That's a lot of extra trash (and the fuel to manufacture and ship it) avoided.
These things actually feel better in your hand too, whether it's the soft cloth ones in groovy colors and patterns or the burlap ones made from recycled coffee bags. Yes, made from used coffee bean sacks; talk about appropriate recycling!
As best I can tell from the Cupcoat Expressions website, there are about 40 different designs to choose from, ranging from $7 to $9.50. They switch out designs seasonally though and you can order custom prints or logos for company swag or a charity event. Starbucks could do this too, I suppose, but they'd probably charge you $20 for one.
These reusable cup sleeves fit most 12 to 20 ounce cups, they're made in Canada, and are biodegradable. This item is right up there with the reusable grocery bag, compact flourescents, and rechargeable batteries: a no-brainer.
Search for more eco-friendly travel gear and gadgets at Gaiam.com