Chacarero is SO good.
The Italian grinder at Coppa is unbelievable if you appreciate an Italian sub with top notch cold cuts.
Umm, surprised nobody mentioned Liberty Bell? Such a good steak and cheese from what I remember. I hope they didn't go down in quality. There are a few locations in Stoneham/Wakefield area.
Also Giovanni's...started in Londonderry, NH now there are a ton of locations, some in MA (they have a website with full list). Their steak and cheeses are amazing!