neiderma@er4.rutgers.edu posted this to rec.games.video.classic:

Playing Auto Racing, on the first track at the beginning
starter position, just drive on the "lower curb" on the grass right
below the road.  Go straight right and don't turn.  You'll drive
all over the "cartridge".

In Armor Battle, you can drive a tank to the bottom of the screen,
and then inactivate it.  Then take another tank (yours or enemies)
and shoot it once or twice to make it move down.  Then re-activate
the tank, turn it so it points straight down, and drive forward
for a minute or two.  The tank will appear from the top of the screen
and the tank will gain some "ghost tank" powers.

vsp@netaxs.com sent me an update for the easter eggs:

Note:  The Auto Racing easter egg is sorta incomplete, as you can go 'off the
course' and onto other courses at many places in the game.  Anywhere where 
there's daylight in between trees is explorable, and often 'hidden' areas
(like the "Drag Strip", a long horizontal area) not mentioned in the manual
can be found.


Intellivision Quirks/Easter Eggs known:
---------------------------------------

Utopia:  On the right island, there is a two-by-three rectangle at the
    upper left.  Just to the right of this block is a one-square bottleneck
    with water directly above and below it.  Sail a boat (fishing or PT)
    as if to sail directly into this bottleneck, and 'push' against the
    resisting sandbar until you're as far as you can go.  Dock (press 0),
    then move the cursor towards the land until the minimum needed to
    control the boat is within the cursor, and select the boat again.
    You should be able to sail directly over the land and come out on
    the other side.

Triple Action:   In the plane game, horizontal-flying bullets headed directly
    at the narrow spot on the upper half of the tower sometimes fly right
    through it, as if the tower wasn't there.

Bump 'N' Jump:  It is possible to jump off the left side of the screen and 
    land safely on the right, or vice versa.

Lock 'N' Chase:  If you stand in one of the tunnels (easiest with the upper)
    and move continuously back and forth while partway off the screen, 
    eventually your thief will travel off the screen and disappear altogether.
    After a minute or two, he will reappear on the other side.

    If you have cleared all the coins in a maze, lock a door directly under
    the top exit.  Run into this locked door from above; you will stick to it.
    Then press up: the level will instantly end without your actually having
    gone out the exit.  (Hey, I never said these were really USEFUL bugs.)

    You will often receive a bonus -- sometimes several thousand points --
    if you are picking up a coin, vault $ or other bonus when you lose your
    last life.

Pac-Man (Atarisoft):  On the title screen, execute the alternate Pause
    command (1 + clear, I think).  The Atari symbol will lock up and become
    extremely blocky, and you will have to reset the game.

    For some reason, all fruits are actually worth double what they should be.

Advanced Dungeons & Dragons:  Move so that a slow-moving monster (on early
    levels, this is all of them, but blobs work best) is above you in a 
    long vertical passage.  Walk downwards until the monster is just barely
    off the top of the screen, then quickly return.  The monster will often
    be cloned; with blobs, you can get up to three at once from one original.
    It takes some practice to get the timing right.

B-17 Bomber:  If you start in practice mode and bomb the living hell out of
    England, the score will run out of numeric characters and start displaying
    text, graphics, and eventually some bonus items from Lock 'N' Chase.