Presumably, you're worried about medium size, 4-legged critters that can actually do harm to you. For everything up to, but not including black bear (wild dogs, coyotes, wolves, etc.), something like a .45 auto is just fine. Beyond that, you are definately pushing the limits of that cartridge.
A large black bear can be well over 300 lbs and is much tougher than the human beings that .45 ACP bullets are designed for. Your minimum choice should be a .357 mag, loaded with hardcast 180 gr. bullets. .41 mag, .44 mag or heavy loaded .45 colt revolvers are much better choices.
If I had to buy a new gun for this specific duty, it would be the Taurus Titanium Tracker, in .41 magnum. This gun has gotten excellent reviews. Plenty of power, very light weight (like 25 ounces), and the porting and excellent grips make the recoil acceptable. Sorry, you're going to have to work on your recoil tolerance if you plan on hiking where the critters bite back.
My own personal choices are:
-S & W Model 60-3 (stainless steel, .357 magnum 3" barrel, adjustable sights) loaded with relatively hot, 180 grain hardcast bullet loads. Kicks pretty hard, but is so nice to carry. This gun is for NON-GRIZZLY country only. I brought it on a trip where I saw 3 grizzlies, and the little gun seemed downright puny. I'll never do that again.
-.45 Colt Blackhawk, loaded with 300 grain hardcast bullets at around 1200 fps. Still, not the best thing to try to shoot a grizzly bear with, but when you can't carry a rifle, its better than a sharp stick.
-Before I got my Blackhawk, I carried my dad's .44 Redhawk, with nearly equal power loads.