Cafe Santropol has amazing sandwiches http://www.santropol.com/
Laika is a nice mellow spot with good food and good music http://www.laikamontreal.com/
Both have free wifi through http://www.ilesansfil.org/
Schwartz's is an old Montreal institution for smoked meat sandwiches http://www.schwartzsdeli.com/
but if the lineup is huge go across the street to Main Deli Steak House (3864 Saint-Laurent)
For great Portugese check out Coco Gallo and Coco Rico.
There's an amazing variety of really good restaurants in Montreal, I'd recommend having a look at http://www.montrealfood.com/index.html about 10 years ago
Ty breize is a good restaurant for britanny style crepe
Soupe Soup is very good soup and sandwich place
Frite alors! is a nice fast food chain with belgian fries and killer poutine. Do not go at the one near berri-uqam.
Bombay Mahal is very good indian food restaurant. Service is horrible however. It's still worth it.
Juliette et Chocolat is an awesome dessert and crepe place. Try the old style hot chocolate.
Les belles Soeurs is a neat sit down fastfood place in the Plateau
Try the "brioche beauté" for breakfast at Eggspectation. This is a chain. quality is uneven.
All these places have low to cheap prices about 10 years ago