Black coffee is naturally low carb - it has zero carbs and zero calories. Unfortunately, most people dump tons of sugar into their coffee drinks.
The first thing to do, of course, is to ask for a sugar substitute. Surely every restaurant I've been to in the past few years has stocked Sweet N Low and Splenda along with its sugar packets. Simply put a zero-carb sweetener into your coffee. There's no reason to add raw sugar into this drink.
Next we hit milk. Milk isn't exactly low carb. However, cream is! If you go with regular cream in your coffee, you're down below 1g for your average addition to a cup of coffee.
I would really suggest you train yourself to drink decaffeinated coffee if you are a coffee drinker. Studies have shown that drinking caffeine raises your blood pressure, and also raises your resistance to insulin. Neither of these are healthy for you. For some people, caffeine leads to headaches and lower fertility rates.
I'm a big fan of coffee drinks for desserts. For example, Irish Coffee is a mixture of decaf coffee and Irish Whiskey. Add in some whipped cream - it has about the same carbs as heavy cream, so relatively few - and you're all set!
Lisa Shea's Library of Low Carb Books