We should probably start any intelligent discussion of a word with its literal meaning. Here is the definition of the word gonzo from the Oxford English Dictionary:
Origin: 1970's: perhaps from Italian gonzo 'foolish' or Spanish ganso 'goose, fool'
I think three of the words that really hit home from the above definitions are Exaggerated, Bizarre, and Crazy. In fact, most examples of gonzo gaming fit most or all of those descriptive adjectives. Here are some examples that come to mind when I think of gonzo:
Greyhawk supplement: pp. 61-63. These pages describe an incredible array of exaggerated, bizarre, and crazy traps and monsters. How about "A troll with a magic spear riding a Purple Worm!" Or "A cloud giant riding a tyrannosaurus rex." Or "Room complexes which are all parts of a monster, the first room being the mouth, the next the stomach, and so forth." Weird stuff!
Arduin Grimoire - the entire series. This runs the gamut, including a class called Technos that can use modern weapons and, at the highest levels, create atom bombs. A gonzo monster example is the Thunderbunny, which is essentially a killer jack rabbit. Better yet, there is a Special Abilities Chart that all PC's roll on. This can get you plum results like "Flesh tastes bad to monsters - 75% chance they'll spit you out!"
As for modern products, I consider the Dungeon Alphabet a bit gonzo. Some of the entries are indeed exaggerated, bizarre and crazy - and I mean that in the nicest way! How about kobolds who worship the "Trash God," who is actually an ancient Neo-Otyugh. Or a pack of aristocratic and well-mannered ghouls who invite the party to dinner - "one way or another!" Great stuff, by the way. I get a lot of inspiration there.
What are some other great examples of gonzo in old-school gaming products? What about more modern RPG's? What does gonzo mean to you?