I use a Hyperdyne and am very happy with it. There is also ROM FX, TRIK TOYS, and some newer options. I would recommend ROM FX or Hyperdyne myself. I am not hugely familiar with the other options, I just know those who have them love them. I have heard bad things about TRIK TOYS though.
Fans are a must! I have a fan kit made from Skullworx. I just bought another too for my other helmet.