21st does a great job of serving interesting, globally-conscious, well-made coffee and espresso. They also provide free wireless and have decently spacious upstairs seating. So far, they make the best espresso I've had in Pittsburgh!
One small gripe: whyyyy oh why is the bathroom always locked? I'm all for a customer-only policy, but having to get the key over and over when studying (and drinking coffee!) for several hours can get painstaking.