If you're still on the fence over whether or not you want to play Diablo III, Blizzard is offering you your first taste for free. The brand new Starter Edition is available exclusively through Battle.net, and lets you play all the way to Act I's Skeleton King boss - and ding up to level 13 - without having to hand over any cash.
The free Starter Edition is available in a bunch of ways:
There's also a third option - if you don't want to have to download the entirety of the game files, simply grab the Diablo III disk from a friend (or an enemy, doesn't really matter), install the game and then log in with your Battle.net account. Through the wonders of modern technology, the Starter Edition will be added to your account!
It really is that simple. The Diablo III Starter Edition is restricted in a handful of ways, some game features are unavailable, that sort of thing. But! If you decide you like this whole "Diablo III" thing, and upgrade your Starter Edition to the full version of the game, all of your progress and achievements will be carried over and you won't have to start from scratch.
Want more information? Head to the Diablo III Starter Edition FAQ and read up, then go grab the files and start exploring Sanctuary for free!