For authors who don't know how to access other distributors, draft2digital.com is a retail distributor that gives you access to a global market, including places like Amazon, Kobo, Barnes and Noble, and many other international retailers. If you do opt to use Amazon, you're better off uploading directly through KDP because you'll get more royalties. (It's like a 5-10% difference iirc, which for me is about 20 cents. Which isn't much, but when some of your royalty checks are literally a penny, that 20 cents matters.)
They recently acquired Smashwords as well and are constantly expanding their global market and library distributors.
(If you want to see how many retailers you can reach with them, this is where you can get my books. I'm in over 20 global stores and need to actually update the listings to include more. Unfortunately, I can't afford to avoid Amazon because, as @derinthescarletpescatarian pointed out, it's really hard to get people to change their buying habits, and I like being able to afford food.)
It used to just be for ebooks, but they now do their own paperbacks that give you the same access as the Ingram Spark market and, unlike Ingram Spark, haven't completely trashed their customer service.
The only downside to avoiding Ingram is that it limits your market for hardbacks unless you're willing to use Amazon, though hopefully, D2D will start doing hardbacks soon. (There are a few other places, but they don't have the same market reach as Ingram, sadly. Yay... monopolies...)
They also partner with FindAwayVoices for audiobooks, which gives you access to a wide global market as well. Like D2D you can access Audible through Findaway, but like Kindle, you'll earn more if you upload directly to Audible.
So, yeah, you want and can afford to avoid Amazon as an author? Draft2digital is the place to go.
As a reader, check the links authors post.
Usually, you'll see Amazon listed, but a lot of us are really doing all we can to be available in as many stores as possible and would LOVE for you to use them.
Please. We're begging at this point.