1900 Jean-Talon Est
I have been there a few times and the food is always excellent and the owner and his mother really nice!
It is just a block away from Metro Fabre, so perhaps a bit of a trek from downtown, but in my opinion worth it. They are from the Isan region and have a whole page of specialities from there on the menu (I think I have ordered almost exclusively from this page).
They have Bankok style AND Isan style papaya salad, a variety of laabs, delicious grilled sausages and a selection of curries. Everything I have tried has been wonderful, I want to encourage everyone who likes Thai food to go there because they really deserve success.
The only downside that I can think of is that they are closed Sundays...