Bonjour comes immediately to mind--pretty nice pastries, sandwiches (I enjoy the croque monsieur), coffee, lots of lingering.
Sit Down Cafe isn't bad either, for lighter options, and for a later lunch I'm sure they wouldn't mind some sitting around. There's also a gelato place just across 53rd and east a bit that isn't bad. I like the very light, very thin 'pizzas' at Sit Down, and they have fruit and terra chips as sides to their sandwiches.
Div School's Cafe (Grounds of Being) is in the basement of Swift Hall, but they're only open until maybe 3.30 or so, though they offer lots of food options from local restaurants. I frequently lunch there.
Not exactly light fare, but I adore Valois, too, and lingering is encouraged. There's even a book written about it. I enjoy the old school, middle American fare. I'm not sure they have things like salads.
Bonjour Bakery & Cafe (in the strip mall, just south of Treasure Island/next to Walgreen's)
1550 E 55th St Chicago, IL 60637
(773) 241-5300
Sit Down Cafe
1312 E 53rd St #1 Chicago, IL 60615
(773) 324-3700
Swift Hall (Div Cafe is in the basement)
1025 East 58th Street Chicago, IL 60637
Valois Cafe "See Your Food"
1518 E 53rd St Chicago, IL 60615
(773) 667-0647