If by "throwing" you mean "launching an accurate projectile", then contrary to most of the other answers here, I'm going to say limbs aren't necessarily the best way to do that.
Captive Octopii, I've heard, can quite accurately hit objects or people with jets of water they spray out of their tank.
So imagine a creature shaped like a bulbous but extremely muscular cylinder, at the center of which is a fluid-filled tube (I guess they live in a water-rich environment, to be able to replenish this easily).
Creature swallows projectile, positions it in tube, and then does a whole-body spasm, generating for a brief moment intense water pressure that launches the projectile just like a cannon would. Aiming still requires a degree of skill, but very much less so than coordinating the multiple joins of a hand, arm, shoulder, and torso, as we do when we throw.
So, mostly it needs good binocular (or multi-ocular?) eyesight with widely spaced eyes to aim at its target accurately over long distances, and good proprioception to align its body accurately. (Not "eyes on stalks" like a snail though, unless they're rigid - eyes that move relative to each other or to the creatures head would make accurate aiming very, very much harder).
Air based propulsion is also possible, especially if we're only considering lighter projectiles. Even with our quite limited chest strength and lung capacity, humans can fire blow-gun darts 50 or 60 meters (according to the first couple of videos that came up on youTube when I searched, anyway), and we're in no way particularly evolved for that. So 100m seems very reasonable for a large, powerful creature to launch small rocks or pebbles via gas or lung pressure, if specifically evolved to that task.
The key physiological trait would be a long, completely straight tube, that acts as the "gun barrel" for the projectile.
If it's inside the creature's body, surrounded by enormous compression muscles, then we might imagine a very heavy, long, lumbering, inflexible creature like a very elongated and stiff hippopotamus. Perhaps on 6 or more stubby legs? It's back-end and middle might be much larger than the front because that's where the most pressure needs to be. And it would aim by positioning its whole body.
On the other hand, the firing tube could be more external, like some kind of protruding horn (using a horn would mean that the projectile would need to fit the bore quite closely, as horn isn't flexible, but maybe it can afford to be picky about the rocks it picks up... or maybe it grinds them down to the right size against each other in some kind of body cavity?). I'm imagining something between a narwhal with legs, and a ridiculously exaggerated rhino (with a single very thick horn several meters long/high).
For smaller projectiles, wind speed might affect accuracy significantly, so these creatures might have large flexible spines or projections, covered in membranes or something like feathers, with which to sense the wind. Perhaps running in a ridge along their backs, or protruding from their heads?
Also if you like, for greater lethality from smaller projectiles, perhaps the creature coats its projectiles in poison? Curare-dipped darts worked for Amazon tribespeople, after all.