I'll start:
>Marx
Too easy, I'll pass this one.
>Keynes
For obvious reasons. Never understood time preference, business cycles, or basically anything. Criticized Mises for being unoriginal despite the fact that his German was, by his own admission, not good enough to recognize an original thought. Member of not one, but two shady, libertine societies. Only saving grace is that he criticized the horrendous conduct and ignorance of Woodrow Wilson after WW1.
>Galbraith
Claimed in the 60's that public services were atrophied because they didn't have enough funding. Also claimed that the market creates its own demand, unlike the government. Apparently, bringing democracy to countries that the average American cannot even spell is fulfilling real demand, whereas if you buy a can of Coke, it's only because you have been indoctrinated by a 30 second clip of some mascot drinking coke. Also said that East Prussia ought to be "euthanized".
Alfred Marshall probably belongs on this list too, but I haven't read much about him yet. I know he was the mentor of Keynes, but not what his theories were.