Apple Systems:
 
           128k->Mac SE Hardware Etch
Here’s a neat little one.  On all Apple computers from the original 128K Mac to the SE is a peculiar easter egg.  The Mac designers decided to gain some fame and glory by having their signatures etched in raised lettering inside the rear part of the Mac casing.  Look closely and you will see all 47 Mac team members on the box of the computer.
 
           Apple IIgs      "Cortland"
            If you hold down (I think) Shift-Option and select the Apple menu and the 'About the Finder' option, it will turn the ENTIRE SCREEN upside down and stay that way until you click the mouse. (Interestingly enough, the mouse cursor inverts and moves in the inverse direction).  Apple IIGS video cards:	Gumby, Pokey (one of these became the Video Overlay Card)
 
           Macintosh Plus     "Mr. T"   
          Entering G 40E118 into the debugger will give you a tiny “Stolen from Apple Computer” message in the upper left-hand corner of the screen.
 
          Macintosh SE           "Z^2, PlusPlus, Aladdin, Freeport, Maui, Chablis"
          Press the interrupt switch (broken circle on the back left side of your Mac).  Upon doing that you will see the debugger in which you enter G 41D89A.  You will then see pictures of the Mac development team.  Reboot to get out of it.

Entering G 4188A4 into the debugger will give you a tiny “Stolen From Apple Computer” message in the upper left-hand corner of the screen.
 
          Macintosh SE/30 (with MacsBug loaded) "Green Jade"
          Press the interrupt switch to get into the debugger.  Use the command DMA 4082E853 20 to display a few bytes of memory from location 4082E853 onwards.  The bytes spell out in ASCII, “WHAT ARE YOU STARING AT?”.

On an SE/30, go into MacsBug or the interrupt debugger, and type G 04D98A.  I have no idea what that does.

Also, type G EB1000 into MacsBug or the interrupt debugger.  This displays the "Macintosh SE/30 Engineering Hall of Fame".  Entering pc=E11000;G works too.  The only way out is to press the reset button.

...Or try this:
The ingredients:
  -One Macintosh SE/30
  -System 7.0 or 7.0.1
  -Kerry Clendinning's "Easy Keys 1.5" Control Panel, or any other
   INIT/FKEY that patches _Launch, like OutToLaunchFKEY or LaunchFinderFKEY
  QUED/M 2.09 (The text editor from Paragon; little brother of NISUS)

Assign some key combinations in Easy Keys Control Panel.
Launch QUED/M, and press the key combination.
Then, an "address error" bomb alert comes up, but you can click on
"Continue" to keep going -- go ahead and click "Continue".

Everything is normal again until you quit QUED/M, at which time the
screen blanks to all white except for a Mac icon and a "Mac SE/30
Engineering Hall of Fame" list.  The same one from above!  That’s kind of wierd.
 
          Macintosh Classic "X.O."
          Hold down Command-Option-x-o as you start up.  If you wait long enough-not too long!, the Mac creates an internal ROM disk (System 6.03, Finder 6.1x, this version is not recommended for the Classic so I don’t recommend you use it for any work.).  If you then use a utility like ResEdit that lets you see invisible folders, you’ll see a list of people who worked on the Classic in the ROM’s system folder.  Mac XO was chosen because the that was the development name of the computer.
 
           Macintosh IIci "Aurora II", "Pacific"
          Set the date to 09/20/89 (release date), set your monitor to 8-bit color, restart, and hold down Command-Option-c-i as you reboot.  A color picture of the machine’s design team appears.  Click to continue.
 
           Macintosh IIsi "Erickson", "Raffica", "Raffika"
           Enter the debugger and type DMA 4086F088 20.  The bytes there spell out "SO...WHAT ARE YOU STARING AT?" 
 
           Macintosh IIfx "F-16", "Stealth", "F-19", "Blackbird", Zone 5
           Set the date to 03/19/90 (its release date).  Then restart with Command-Option-f-x.  You will also see a picture of the design team.  Click to continue.
 
           Macintosh LCIII
           Type DMA 40843B38 190 to see “Life is Good” repeated.
Type DMA 4088A1E8 999 to see “Yeah” repeated.
Type DMA 4088B0E8 999 to see “Neat” repeated.

At DMA 408D3B68 200  to see a bunch of initials starting with “SLRWHBB...” and finishing with “Mon. Oct. 21, 1991”

At DMA 408EFFF8 999 you will see the same initials as you would on the Powerbook 170 starting with “HJR...” but finishing with “Mon. Oct. 21, 1991” (Probably the date the ROM was hooked up)
 
           Powerbook 170 "TIM"
           Type DMA 40843B38 190 to see “Life is Good” repeated over and over again.
Type DMA 40889798 999 to see “Yeah” repeated.
Type DMA 4088AED8 999 to see “Neat” repeated.

...And if you type either DMA 408CA958 999, or DMA 408D8FD8 999 you will see a list of, I think, initials starting with “HJRBGMSH” and finishing off with “Tue, Jul 18, 1989” repeated over and over again.  This was probably the date that the ROM was hooked up.
 
          Quadra 840AV (may apply to other Macs) "Cyclone"
          In the debugger, preferably MacsBug, type DMA 40811FE8  240 to see a large bunch of credits for the “The Super Rom™ Super Team”.  This includes the credits for Central, RISC, MSAD, Cyclone, and a special “thankzzz to all who contributed to past ROMs and system 7.x.”

Type DMA E67E5E 999 to see the name Caro Enricuccio repeated.
Type DMA E67E5E 999 to see “Ah Que Coucon” repeated.  (I believe this is in another language in english writing due to the fact that ASCII on an American computer can only use English words)
At DMA E5E83E 100 you will see a bunch of random and wierd words combined.  This is what you see: “Peace, Cow Boys, Frogs, Sayanara, Krisprolls, No Maastricht, Vikings, Reindeer, Kurtoffein, Bowler Hats, Spaghetti, Dykes, Cead Mile Falte, Siesta, Kiwis, Bankers, Chocolate, Aussies, King Kong, Kim Li Sung, Sand O Kan, Equator, Made in, Sylvie Vartan, Praha, Tatra.”

All three of the above are in the modem section of the ROM, which may or may not have any significance.  I have a Geoport Modem which uses Express Modem software, if that helps.  All I can make from this is that some of the development was done in Japan or in another country and that they left some marks of their own in the ROM.
 
            Performa 6115CD
            Typing DMA 3A091 50 or DMA 3E4F1 50 in MacsBug will bring you to two locations where it says “Ol’ McDonald had a Farm... It’s also a bitch, then you die too!”  Seriously, I don’t even want to know.

Type DM 642F1 in MacsBug to see “Flush to Execute”

Type DMA D13E1 999, DMA EA811 999, DMA EB111 999 or DMA 40A98202 999 to see a big list of common phrases, credits, and awkward humor.  For example, you will see anything from “Huck and Hil are Cool Managers” to “0wdered 4oast -an” (that means “Powdered Toast Man” from the cartoon Ren and Stimpie) in ASCII.  It is all broken up with numbers and symbols but for the most part it is pretty much readable.  Need I add that it finishes with “Joy!”.
 
          Any Macintosh computer
Every Mac will play interesting noises if it fails its internal RAM check.  You can harmlessly force it to fail its check by pressing the Interrupt button on your system immediately after it starts booting up.  Mac II systems play interesting chimes, Quadra AV's play drum solos, LC's play a flute, and the Power Macintoshes play a sound of a car wreck with glass breaking.