All of these suggestions are good, but I have found that companionship, in addition to location, is key to seeing wildlife. If you are traveling with at least another couple (or children) you have more eyes available for spotting. Top wildlife sighting trips for us have been tours to the areas listed above.

Glacier, Denali, yellowstone, tetons, jasper, banff in that order close enough, but it really depends on how you spend your time in these parks.

drive bys vs. back country or hiking trips. Glacier gave me both but i was there for two weeks! Denali not as much but i was only there for 3 days.

on my trips:
From your car in glacier (or at least at the pull outs along the way) you can see mountain goats, grizzly,black bear, big horn sheep hawks eagles

from the car in denali (or the bus) dahl sheep, grizzly, moose, coyote hawks eagles

from the car in yellowstone elk hawks eagles deer coyote moose