1. InvisibleShield – good not great, but slightly expensive.
2. Purplemoo.com – another ok option, but not very durable.
3. Daproducts.com – good quality, but very difficult to take off – the material is hard and somewhat semi-permanent.
4. Navprotector.com – lasts much longer than some of the others and relatively cheaper. I use these guys and am still happy after a good two years.
Hope this helps