The FURminator is the most recommended pet brush I've ever heard of. I've had wonderful results with my small to medium sized pets.
In addition to the giant Great Pyrenees that bosses me around, I have a Cavalier King Charles Spaniel and a Maine Coon Cat. While not as crazy in volume as the Pyr, their long hair manages to get into everything too. The Pyr, clearly, takes some special brushes, however I've found that the FURminator does an amazing job on the smaller guys.
Essentially an undercoat rake with the sides of the tines mildly sharpened, the FURminator pulls and cuts dead hair that is ready to come loose. Be careful as it is both pointy and possible to get loose skin caught between the tines, though unlikely. After each stroke you'll likely have to empty the tines, which is simple with a press of a button. The brush pulls loose that much hair. You'll have piles of it very, very quickly. Shocking amounts. Like a pile the size of the animal you are brushing.
The Medium Dog/Long Hair brush seems to be identical to the Large Cat/Long Hair brush. I use the one for both.
A weekly brushing with this keeps the Maine Coon pretty much perfect and I rarely see a hairball. Heart, the cat, had lots of hairball problems when we got him from the rescue. Pretzel, the Cavalier, has fur like a cotton ball. Like magic, she picks up leaves, sticks, twigs and all sorts of tangle making nastiness on every walk. The FURminator really helps take the frizz out of her fur, keeps mats from forming and makes it a lot easier to remove the errant tree branch.
The undercoat rake I use on Nemo, my Pyr, does nothing for the little guys. The tines are too big and far apart, its like dragging a spoon through their fur. For the smaller/medium size animals the FURminator is great. On the Pyr, even borrowing a Large Dog/Long Hair variant, is pretty useless. The brush gums up with hair in about 2 inches and is jammed in Nemo's fur. He generally loves the rake and will lay around, moving to direct where I brush, for hours if I'll do the work (longest time brushed? Das Boot, directors cut.) Nemo hates the FURminator and would head for another room after the first few tries. Honestly, a Pyr has pretty awesome and unique fur for a dog, it is no surprise. I'd doubt the FURminator would be much use on dogs like St. Bernards or Bernese Mountain Dogs, but likely would have worked on my Malamute.
I'm a huge fan of the FURminator. It is no surprise, everyone raves about it. The brush is on the expensive side but $25 for the Large Cat/Medium Dog sized one is reasonable. Please make sure you get the right one for your size animal and that it is compatible with your dog's coat.
