Bowker
Buy your ISBN directly from Bowker – every ISBN in the world comes from them. An ISBN is a number that uniquely identifies a book. You will need one ISBN for your paperback and another for your eBook (no matter the file type – Kindle, Nook, iBook, etc.).
CreateSpace
CreateSpace was merged with Kindle Direct Publishing the end of 2018.
Kindle Direct Publishing (KDP)
This is where you setup your paperback and eBook to be on Amazon. It has a wonderful online interface that allows you to see what your printed book will look like. You will also be able to order paperback books for proofing and later for shipping to friends/family at the best price. No up front costs – they only collect royalties.
This requires you to upload your manuscript .pdf file for the paperback (created in MS Word). For your eBook you have two options – you can either have KDP create your eBook for you or you can create your own using Jutoh. In the latter instance you will need to upload your .mobi file (created in Jutoh) to KDP.
Advanced marketing …
Apple iBook
This is tricky. You will either need to know someone who has a mac computer, or use a cloud service to upload your book to iTunes. I use MacInCloud.
Barnes & Noble Nook
Nook is B&N’s equivalent to Kindle which has no up front costs. B&N also offers paperback and hard cover services, but there is a hefty up-front fee for these.
Nielsen BookData
Based in the UK – the world’s leading book marketing agency. They sell to book buyers and libraries.
IngramSparks
EVERYTHING in the United States gets printed here, no matter where it’s ordered from (Amazon, B&N, etc.). I recommend doing this after you’ve had your book out a while. Ingram will expand your book availability to around the globe which will include libraries and schools. They also offer hard cover options.