Amazon Prime members can choose one of six free titles published by Amazon (it's the monthly Kindle First offering), but for the rest of us there are also a couple free ebooks
For example, Amazon's monthly free Kindle+audiobook bundle for September is The Phantom of the Opera:
Far beneath the majesty and splendour of the Paris Opera House, hides the Phantom in a shadowy existence. Shamed by his physical appearance and feared by all, the love he holds for his beautiful protégée Christine Daaé is so strong that even her heart cannot resist.
If you are unable to get the Kindle+audiobook offer, you can also find the ebook just about everywhere. LibriVox has the audiobook.
And if classic horror is not your thing, Macmillan is giving away a free ebook this month via the Tor.com ebook club.
This month's free ebook is Gardens of the Moonby Steven Erikson:
The Malazan Empire simmers with discontent, bled dry by interminable warfare, bitter infighting and bloody confrontations with ancient and implacable sorcerers. Even the imperial legions, long inured to the bloodshed, yearn for some respite. Yet Empress Laseen's rule remains absolute, enforced by her dread Claw assassins.
You can download the ebook by first giving Tor.com your email. This freebie is supposed to be limited to NA, but they're not geo-blocking so it's really available to all.