Update - May 17, 2003: this café is closed right now - the building is going through major renovations! Likely not to be closed much longer, though. In the meantime, there's Cafe Strindberg just a block further along the Esplanade!
This is my favorite café in Helsinki. And, judging by the huge lines that sometimes go all the way to the street, it is the favorite of a number of others, too . . .
Getting a table outside in the summer requires some mean elbowing, but it is the best place in Helsinki to sit down and see people!
The café offers specialty coffees of all sorts, brewed tea (several varieties), iced tea, freshly squeezed fruit juices, wine, and spiked coffees, too. They also have soups, salads, paninis, and sandwiches (of the quite delicious fresh mozzarella, basil, and tomato foccaccia variety).
The "pulla" (sweet baked bread, kind of the same as cinnamon rolls) is great--and extremely large--you'll need to share it!