Tazza D'Oro is by far the best coffee near Carnegie Mellon, and has great sandwiches and pretty good pastries to go with.
Tazza's brewed coffee ranges from good to excellent, depending on how fresh and which blend it is. It is where I first learned to drink my coffee black and appreciate the interesting flavors in the coffee instead of just drowning it in milk and sugar to hide the coffee for the sake of the caffeine. Their lattes are strong and wonderfully bitter, but don't have the overly-dark, burnt flavor that some have. They also have a nice selection of teas, although I haven't tried most of them.
Tazza also has a great selection of panini, often made with local ingredients. My favorites are the roast beef and the portabello mushroom; at one point they had (and periodically still have) an absolutely excellent ham, apple, and brie sandwich. They're a little pricey, but if you skip the (tasty!) side salad, you can save $2.
Their pastries are pretty good. There seems to be some contention as to whether they're made by Tazza or not; I'm not sure if they're *assembled* locally, but they are certainly *baked* locally. My favorites include the cinnamon scones, the brownies, and the apple tarts.
Tazza is on the CMU dining plan; it's probably one of the best values (in terms of quality, at least, if not quantity) for a lunch block. As a consequence of this, though, they do accept credit cards, but only Visa and MasterCard.