Fossils, people! FOSSILS! Rare and extraordinarily preserved fossils.
Redpath is located on the McGill University campus. Entry is free and the museum is small. The main focus is on rocks and fossils.
The have minerals from Quebec, a mummy, fossils of dinosaurs, and strange animals. The "back to sea" exhibit has a great collection of fossils from the water and the "Dawson gallery" has a collection of strange animals that played connecting roles in evolution.
The museum is small and doesn't take much to tour but, the collection is definitely worth visiting.
Oh, and a bonus (if you go in the summer), is all the half-naked guys playing frisbee on the McGill university lawns. Bonus!!