Try The Etched City by K. J. Bishop, which has a wonderfully hallucinatory feel to it, not least because the protagonist is often on hallucinogens. Dhalgren by Samuel R. Delaney is trippy to the point where I have no idea what it's about. The aforementioned Illuminatus Trilogy is brilliant as well, and The Invisibles, a comic series by Grant Morrison.

If, however, you mean "bizarre and random", you might like Carlton Mellick III, whose books have titles like Razor Wire Pubic Hair, Satan Burger, and Electric Jesus Corpse, and whose contents reflect and supercede the titles, though I've only read Razor Wire, about a prostitute robot in the future.

Here's an extract from Satan Burger:

God hates you. All of you. He closed the gates of Heaven and wants you to rot on Earth forever. Not only that, he is repossesing your souls and feeding them to a large vagina-like machine called the Walm - an interdimensional doorway that brings His New Children into the world. He loves these new children, but He doesn't love you. They are more interesting than you. They are beautiful, psychotic, magical, sex-crazed, and deadly. They are turning your cities into apocalyptic chaos, and there's nothing you can do about it ...

There's also Steve Aylett, whose Atom is fantastically weird and imaginative.

Also there's books that defy description, like House of Leaves by Mark Z. Danielewski, a postmodern horror story (maybe) The Book of All Hours By Hal Duncan, a sci-fi fantasy epic (perhaps), and The Raw shark texts by Steven Hall, about amnesia, love, and aquatic conceptual predators.

Finally, to answer your question; Phillip K. Dick.