Try looking in the Easter Egg archive.
Many authors put in jokes for their own amusement. Wilson “Bob” Tucker used to put the names of friends in his books so often that it gave rise to the term “tuckerization.” A friend of mine has been tuckerized in one of Anne McCaffrey “Dragonriders of Pern” novels, for instance. Sometime authors use this as a way to raise money for charity – the highest bidder gets tuckerized.
Some other examples:
“The Starcrossed” by Ben Bova is one big in-joke about the making of the TV series “The Starlost,” including a portrayal of Bova and Harlan Ellison, who were both involved.
The name “Ford Prefect” in “Hitchiker’s Guide to the Galaxy” is – well, it’s an in-joke to U.S. readers, though very obvious to British readers. The Ford Prefect was a car model popular in Britain; a rough U.S. equivalent would be “Ford Escort.”
In the fairly obscure young adult novel “Trying Hard to Hear You,” by Sandra Scoppettone, all the characters are roughly based on actual people in the town at the time (I was one of them). Scoppetone was director of a performance of “Anything Goes” and used that for the novel – maybe too much so.
The creepiest in-joke was in a James Tiptree, Jr. story about a character who committed suicide by shooting himself in the head and discovering he was in a wonderful version of heaven. It was published postumously, after Tiptree had committed suicide with a bullet to the brain.