Mario Kart 64

Race yourself:  If you can complete the Luigi Circuit in under 1'52"
you can race against yourself.  You need only do this once, as this
"ghost" player will be saved to memory.

Reverse course:  To race any course in reverse, just get a gold in 
all of 50cc, 100cc, and 150cc races.  You'll know when you have when 
the title screen changes.

Turbo start:  Start the race and watch the lights carefully.  Press A 
as soon as the second light dims.