The Jokermobile was used throughout the Silver Age as the Clown Prince's mode of transportation.
In Gotham City Sirens #5, Harley Quinn mentions that Joker had retired the car out of embarassment around the time they started dating.
Though it's had many different forms, the Jokermobile's most famous look was a purple car with a larger version of the Joker's smiling face was mounted on the grille.
In the comics, the Jokermobile seldom appears as more than a customized car. However, in later appearances, it has been shown with a spring-loaded boxng glove in the trunk and an ejector seat.
In earlier appearances, the car had a "bridge-building" feature, allowing it to create bridges to drive on.
In Batman: The Animated Series (and sequel series "The New Batman Adventures"), it had a large missile rack in the trunk at a false rear half that could detatch (with the real rear half beneath it) which allowed it to escape the Batmobile's grapple.
In "Batman: the Brave and the Bold", it had a large hot air baloon to deploy if it's wheels were taken out, as well as four large springs. It's weapons included two mechanical arms in the trunk that squeeze a giant whoopie-cusion, creating a compressed air blast (powerful enough to knock Black Manta's tripod off a cliff); can fire an oversized jack-in-the-box from the "mouth" of the Joker face (to distract the coulrophobic Guy Gardner), can launch a giant Joker Fish from the side (smashing the Batmobile's windshield), and has a giant flower that sprays acid (used to destroy the tires on the Huntress's motorcycle).
In Other MediaEdit
The Jokermobile has appeared in the 1966 Batman Television Series as a modified dragster, Batman: The Animated Series as a simple purple car (though the episode "Joker's Wild" featured one that resembled a purple golf cart with Joker's face on the front), and "Batman: the Brave and the Bold".