Looking through these Joker Costume pictures will let you see some examples and give you some good ideas so you can decide what costume is best for you to wear on Halloween.
Here's a great Heath Ledger type Joker costume from The Dark Night.
Here's an old school Joker costume.
Here's a classic Joker costume with purple suit.
Here's a homemade Joker costume.
Here's a group of different types of Joker costumes.
Here are traditional Joker and Harley costumes.
Here's a DIY female Joker costume.