* A troop of monkeys (the most common way to refer to a group of monkeys)
* A bunch of monkeys
* A horde of monkeys
* A crowd of monkeys
If you're talking about monkeys in a more specific sense, like a large group of monkeys all in one place, you could also use:
* A congregation of monkeys
* A gathering of monkeys
* A mass of monkeys
Ultimately, the best way to describe a heap of monkeys depends on the context and the desired effect.