There are several different types of air intakes but they tend be rather pricey, generally around $250-$300. I had modified my intake slightly on my first Nomad, but it provided little, if any, performance improvement.
I didn't care for the looks of the hyper-charger, nor the tornado/spiked air kits, and I had pretty much decided to go with a Barons Big Air Kit, until I heard of Joe Norris and his kits. Joe Norris (CHUCKSTER)is a machinist who makes beautiful custom accessories.
I decided to get Joe's double, and then later went with his single plate kit. The double plate kit allows you to continue to use the stock "dog bowl" cover, and is a bit quieter, but the single plate is more free flowing and more custom looking.
For $100 this intake is an amazing value and adds a tremendous performance increase to the bike.
To check out more of Joe's stuff, go to http://www.chucksterscustoms.com/Products