I always use an Aquarian Port Hole. You can check it out here:
Usually what I'll do is adhere the port hole to the inside of the front head and slowly cut around the inside of it with a utility knife. They're nicer because your front head will be protected. I've had front heads rip from either a soundman or band member yanking out the bass drum mic at the end of a show when we'd tear down. They're definately worth the couple bucks they cost.
Remo makes one too called a Dynamo, which are the same thing. I've used them too when the music store didn't have the Aquarian ones.