Audible + Amazon have a promotion where you can get a free physical book and 2 free Audible audio books if you sign up for a free 30-day trial.
If the book is eligible you should see a banner above it with the promotion. You might have to refresh to get it to work. I posted a picture of what it looks like. I believe the maximum amount is $50, but someone said they got something for a little more. The book has to be sold by Amazon.com from what I can tell.
I want to maximize the deal so I was thinking of getting box sets. Please put your recommendations in the thread. I wanted the Calvin and Hobbes collection, but it seems to be just out of the maximum amount. I might get the Scott Pilgrim set, but the hardcover Watchmen graphic novel looks cool too. I was also thinking of a nice hardcover coffee table book or cook book, but I have no idea where to even start.
The only book sets I could think of were Harry Potter and Lord of the Rings, but I already have HP on Kindle and don't really like fantasy.