Shepherds are herding dogs by pedigree, which is how they got their name, and it's hard to find a better mix of brains and brawn. They're tireless workers, extremely loyal, and highly trainable.
Weight: 50–90 lbs.
Best Qualities: Smarts. They're also tough, courageous, athletic, and curious, which is why they're so popular as police, military, search-and-rescue, and guide dogs.
Drawbacks: Dog-show people have screwed up a large percentage of the purebred shepherds by breeding them to have a dramatically sloped back, which gives them an awkward gait. This can cause health issues later in life, and it isn't great for athleticism or endurance, so take a good look at a kennel's dog's history before buying a puppy.
What to Do With Them: They're good runners for their size, and well-equipped for rugged trails and mountain hikes.
Buyer's Guide: The U.S. has two clubs, one for show and one for working dogs. Your best bet for good working dogs is the United Schutzhund Clubs of America.