I drew the outline in Illustrator using an image of the bat symbol from the Batman Begins logo. The ears are a little more pointy than they are on the one Bale makes in the movie, but if you read the excellent The Dark Knight Manual (a must-read for any Batman fan), you'll learn that each batarang was handmade for a different purpose.
Alternatively, you could draw something completely unrelated to a batarang and make a dogarang or a catarang. Whatever your superhero heart desires. There's plenty of room in the JLA for everyone.
If you want to make a batarang, I've included a PDF of the outline I created. Size it to whatever you like. We've made 4", 6" and even 7" batarangs. You're only limited by the size of your donor sawblade (and your skill with a cutoff wheel).