I'm usually purely a 1/72 collector, as far as human-scale minis goes, but since I temporarily have something of a warehouse of all sorts of miniatures, I thought I'd take the opportunity to take a snapshot for the purposes of scale comparison.
These are a little shorter than shown, since they're a few millimeters away from the backdrop, but this should give a relative idea of different scales used in fantasy gaming. To the left is a Reaper Miniatures figure, one of the new Kickstarter Bones. Even though they're advertised as "heroic 25mm," you can see they are quite a bit taller. To the right is a D&D Miniature, from the Dragoneye series. D&D minis are a bit inconsistent scalewise, but this guy is fairly typical.
Continuing to the right is a game piece from the World of Warcraft miniatures game. He's actually about 25mm from foot to eye; I think this puts him in about the same scale as most Games Workshop minis (I could be wrong, though). Finally our old friend Sven the 1/72 comparison viking, who is about 25mm from foot to scalp, making him a bit shorter than the WoW figure. Not shown is an example of a 15mm figure, for the simple reason that I don't own any :). It would be about 1/2 to 2/3 the size of Sven, depending on the manufacturer.