Any list of this sort will be incomplete but this should get you started and give you inspiration!
Basic Marbling Pattern Sources:
The Ultimate Marbling Handbook by Diane Maurer-Mathison (Watson-Guptill, 1999). Diane M-M has written a number of books (some with a slightly different author name) – all are pretty good but this one is the best in terms of pattern descriptions. It has been out of print but is now back in print and available from her in a hardback edition for $60. plus shipping on her website. Sometimes if you “lurk” on the used books sites you can find a paper back for $30-$35.
Marbled Designs by Patty Schleicher and Mimi Schleicher (Altamout, 1993). This book is also out of print, but again, you can sometimes find an used edition for $17-$30 on a used book site.
There are of course other books but these are the two that I have based my learning around. I also go out on Pinterest and often see other patterns. It is fun to try and figure out how they were done and sometimes to attempt to recreate something similar.
Well known U.S. Marblers
Steve Pittelkow Pat K. Thomas (Seenmymarbles = website)
Diane Maurer-Mathison Barb Skoog
Mimi Schleicher Regina and Dan St. John (Chena River Marblers)
Google these people and see their websites, their papers, and YouTube videos.
Marblers Throughout the World
“Cockerell Marbled Papers” on Facebook and on YouTube (title is “The Art of the Marbler”) is a good source for inspiration. Unfortunately this operation is no longer in operation so get those papers while you can!
You can see a very particular style of marbling on YouTube by putting “Ebru Marbling” into the search engine. Mostly out of Turkey, this is where they drop paint onto a pattern they have already drawn and make representational art with a stylus. It is fascinating!
Pernille Snedker Hansen (Denmark) Also see the YouTube video, https://www.youtube.com/watch?v=9ir2vkDJxBo
Antonio Velez Celemin (Spain)
Robert Wu (Canada)
Karli Frigge (The Netherlands) Also see a YouTube video of her work, https://www.youtube.com/watch?v=Gk7QiGzK9tA
The International Ebru Conference (May 2016) lists some major marblers world wide under the subscribers heading http://imcongress.org/en/subscribers.php