Amazon is slooooooooooooooooooooooooowly reversing their massive delisting of Macmillan authors. With great power comes great responsibility, Amazon.
John Scalzi has a very generous post on what you can do to help the authors suffering collateral damage.
They include Gene Wolfe and Charlie Stross, to name two of my favorites, although they probably aren't the ones that need the money most.
Here is a list of authors published by Tor, one of the Macmillan imprints.