The Dopefish in Other Games
Duke Nukem 3D - In the original plans for this game, the Dopefish was to make a cameo appearance before it was nixed by George Broussard. One of the game's characters was to be a shark, and if the game was started with the DOPEFISH command line parameter, the shark would appear as a Dopefish. The sharks were cut from the game, and the Dopefish went too - when the sharks were reinstated before the game's release, the Dopefish was not. The final released version of the game does contain one reference to the Dopefish, as a hidden message reading "DOPEFISH LIVES" in level five of the shareware episode.
Quake - By following a certain sequence, it is possible to find the Dopefish in the 1996 release of this game. A hint reading "the Well of Wishes is in the Crypt of Decay" is given in the shareware episode, and in episode 2, level 3 a small sign reading "in here" can be found, and leads to the Dopefish. There is also a Dopefish card] in a set of Quake-based trading cards released sometime in 1998.
Quake II - The Dopefish can be found in the "Cooling Facility" level of this game. Despite rumors to the contrary, the fish is not dead.
Quake III - A large green fish appears in the game, and while it bears little resemblance to the Dopefish id Software reports that is what it is supposed to be.
Jazz Jackrabbit 2 - This 1998 Epic Megagames release features the line "Spaz ate the Dopefish" but requires an elaborate sequence of jumping on things and shooting various marks. The green monstrosity himself does not appear.
Descent 3 - Before this game was released, the makers held a contest giving individuals the opportunity to send in a picture and character name to have appear as a default character in the game. Someone with the name mscooper sent in a picture of himself dressed as the Dopefish for Halloween, and his submission was chosen. If you make a pilot called Dopefish, the default pilot picture is of mscooper as the Dopefish.
Battlezone - Typing "dopefish" at any success screen in this game's Red Odyssey add-on pops up the Dopefish's picture and biography.
Daikatana - The Dopefish appears at four points in this game: the sewer system, Acropolis, Plague Village, and Tower of Crime. He is actually part of this game, and each of his lairs contains an invulnerability artifact that allows you to either look at him or attempt to defeat him.
Anachronox - It is probably unsurprising that the Dopefish appears in this game by Tom Hall. There are, in fact, three appearances - of baby Dopefish.
Wacky Wheels - Apparently starting any single-player race in this game and following instructions can make the Dopefish appear. When the race starts, the player should not accelerate, but should instead hold down the brake and turn to the left while keeping the lion on screen. After spinning around in a circle for a bit, the Dopefish should appear.
Rise of the Triad - Beginning the game with the -dopefish parameter displays the head of the Skipper from the Gilligan's Island TV series - but no actual Dopefish.
Max Payne - There is a poster in the game that reads "Dopefish Lives!" It can be found by following the instructions at Max Payne Easter Eggs.
Electrode for writing about the Dopefish in Max Payne, and jobby for pointing me to Electrode's writeup.