nitrous express makes the best kits available.
I'd recommend this
http://www.overboost.com/obs/product.asp?pid=20280 if you dont plan on spraying too much more than a 75-100shot(which you wont be doing on a stock engine anyway).
if you run just the 35/50shot you really dont need to buy anything else. maybe some spark plugs that are a heat range colder.