As well as the general craziness of the Illuminatus trilogy, Schrodinger's Cat, and the rest, the following are examples of his more sirius works:
Prometheus-Rising
"a truly remarkable book that will turn your thinking about the world on its head, or at least illustrate how everyone else in the world sees it differently."
Quantum Psychology
"a real eye-opener if you've not read much about human consciousness, the influence of language on our thinking, or on how the mind works."
And for the conspiracy theory fans out there:
Things that ate the Constitution
"How did a Nazi spy come to have an enormous influence on US foreign policy? Will the "war on terrorism" put the last nail in the coffin of the rights of American citizens? Would Hannibal Lecter make a better president that George W. Bush? These are the questions asked in this work, offering humorous dissent and righteous anger in the anti-establishment tradition."