This comedy festival is one of the best. Usually runs mid to late July. Many options for all budgets (some free performances, some paid ones that include some top names). Most of the free ones are in French, so if you don't speak it, that would be a problem.
They range from improv, to international names, to local stars. It is now set up in the Quartier des Spectacles (metro Place des Arts) over several stages. Many of the paid performances are in the nearby venues.
As many festivals in Montreal, they close many streets near the area, so food vendors, street vendors and street performers can do their thing. Lots of great food choices, lots of seating, very well done.