Firstly doing downtown park at Eddy's Parking lot, then walk east down St. Catherine St. If you're single, or out for a bash, try Sir Winston Churchill's Pub. It is a world famous singles bar with a fantastic terrace where you can buy a pitcher of Sangria and watch the beautiful people with their Ferraris, Aston Martins etc, and model-beautiful girls Saturday night. People a little older will like Winnie's upstairs. There used to be a fantastic dance club called September's on Mountain St. south of St. Catherine. I think they changed the name but you won't find a place more chock full of hot dancing babes.
The old main, St. Laurence Blvd. (St. Laurent Blvd en Quebecois), is pretty alive with nightclubs too. You might want to walk north and go to Schwartz's Delicatessen and have a smoked meat sandwich - a true, genuine smoked meat sandwich. Venture east on St. Catherine again and head to St. Denis St. if you want to visit the deep French nightlife area.
Old Montreal is great during the day, especially if you have kids. But if you want a delicious meal the restaurants there are very, very good.
Good fast food for drunks:
Kojax Souvlaki on St. Catherine St. just west of Crescent or...
Lafleur's Restaurants (there's a few of them). Try their Michigan hot dogs. Also, you won't find better fries anywhere.
Then there's Chenoy's Restaurant on St. Jean Rd. just north of Hwy 40 (the T-can) on the left side. Smoked meat pizza there is to die for.
All the SuperSport guys used to park in a row on St. Catherine near this big amusement arcade east of Mountain. At one time you could count 200 bikes on a good night. I think that's all over now but it sure was cool back in the day.
And yeah, Club Supersexe is good but it's pricey. If you want sleazy and easy try the lower Main (St. Laurent south of St. Catherine).