A Rome institution since 1946, steps from the Pantheon. Famous for its granita di caffè — frozen espresso layered with whipped cream, served in summer and one of the quintessential Roman experiences. Also does excellent straight espresso and sells its house-blend beans to take home in distinctive golden tins.
Less of a pilgrimage destination than Sant'Eustachio but equally good for coffee, and more convenient if you're already at the Pantheon.