Barnes & Noble are currently giving away a very nice B&N Classics annotated edition of The Inferno, in the Henry Wadsworth Longfellow translation with the Gustave Doré illustrations.
It's not only got explanatory foot and endnotes for the vocabulary and various allusions, but also comes with a bunch of essays about Dante's life and milieu and the cultural impact of The Inferno.
If you miss it from this week's rotating
Build Your Own Free Classics Library promo, it's also available as part of B&N's
NookStudy welcome kit, which you get access to after downloading the app.
I should warn you that B&N require a credit card # even for free books, because the last 8 numbers are used as part of their social DRM scheme. Also non-US customers will have to acquire a US shipping/billing address of some sort and a US-based VPN IP proxy wouldn't hurt.
But aside from that, it's a really nice edition and well worth the download. They've also a similar version of part 2 of The Divine Comedy,
The Purgatorio, but it's not currently free.