Eating out for lunch can be pretty unpleasant in Stockholm. Below are some of the places that help you escape from such a disaster. (For their locations, use hitta.se to search.)
Canteens (sharing the table with other customers)
La Neta (Barnhusgatan 2, Östgötagatan 12B)
The best among several Mexican restaurants in Stockholm. Try tacos grandes.
K25 (Kungsgatan 25)
Most foodcourts in Stockholm are very much disappointing. But K25 is different, collecting the city's best lunch takeaway chains such as Beijing 8 (Chinese dumplings) and Zocalo (Mexican). Caffe Nero deserves a particular mention, serving decent Italian pasta. Somehow better-tasted than at its original location at Roslagsgatan 4. Closed on Sundays. The only problem with K25 is that its black interior, if stylish, doesn't appeal much during Stockholm's lovely summer time.
Paradiset Foodcourt (Brännkyrkagatan 62-64)
Another foodcourt that is worth being mentioned here. The upstair of an organic food supermarket is devoted to several health-conscious budget eateries. Delibruket Flatbred's pizza is probably Stockholm's best.
Kafe Esaias (Drottninggatan 102)
Perhaps one of the best cafes in Stockholm. Its espresso was once named one of the world's top 5 shots. Lunch is also good. Try grilled sandwiches (accompanied with a little salad). Staff is very friendly, something unusual in Stockholm.
Foam (Karlavägen 75)
The best cafe in Östermalm with wooden, concrete, and shocking pink interiors in harmony under one roof. A bit pricey, though.
Chaikhana (Svartmangatan 23)
A tea house serving an English afternoon tea (a pot of tea together with quality sandwiches and English scorns) in the middle of Gamla stan.