If you're even vaguely interested in Diablo 3, or skill trees, or descriptions of exploding frogs that deal 250-326 fire damage on impact then you'll definitely want to check out the Blizzard's Diablo 3 skill calculator . It details every skill for every class, and, even better, gives descriptions of every possible runestone modification. There are a lot. And they are mad.
You can slot runestones into any power, improving them and changing their effects. We're not talking about adding a little bit of damage, or doing ice damage instead of poison damage, we're talking a the stone that changes the Demon Hunter's strafing triple shot by adding additional homing rockets to the attack. Or there's the stone that alters the Witch Doctor's plague of toads ability to make it summon a "Toad of Hugeness" which will swallow up enemies. Use it to nail down your ideal build before Diablo 3 comes out, or simply try and find the most insane abilities you can. Let us know your favourites in the comments.
The sheer number of skills, and the ability to alter each of them so dramatically with a socketed stone means a staggering number of build options. Diablo 3 will actively encourage you to experiment as much as you want with your character, letting you respec whenever you like without penalty. Read our Diablo 3 hands on preview to find out more about the skill system, and how each class plays.