What are we talking here, hunting or self defense? I know plenty of people that hunt large dangerous game (Moose, bear and the likes) with a bow.

If you are talking self defense I can't think of much that will reliably stop a charging grizzly or larger animal in its tracks before it gets to you.

I would say the biggest gun you can shoot and handle well, even if that means a 30-06 or something similar. My grandma used to live in Alaska and she took a 7mm mauser with her when she was doing chores outside like hanging clothes and what not. I huge gun will not do you much good if you can't shoot it well and quickly.

There is always the trusty 12 ga as well.

Paul