You have a lot of different options. What I would recommend doing is reading over the diff threads in this forum, as well as the iPhone case forum. Also read over reviews from Apple.com. I know it is time consuming but well worth it in the end. Currently on my gen 1 iPhone, I have a power support crystal film to cover the screen, with a black agent 18 ecoshield case. That fits very snug into a clip that I bought with the first case, whose name escapes me.
Take some time reading the reviews, you won't be disappointed. More then likely the most popular and highly recommended ones that you read about from Apples website will be sold out at the store, so try searching for it on amazon. More then likely it will be cheaper and get to you a lot quicker. Hope that helps
i must say, my brother purchased the power support crystal film for his new iPhone when he got it last week, and between the common invisible shield/best skins ever/other assorted screen protectors that share a VERY common design, the power support protector is really nice, and i feel it trumps out the invisible shield design in all aspects.
the power support protector doesn't show fingerprints nor retain facial smudge/oils like the invisible shield does. it also has the added perk of having the anti-glare stuff, which the invisible shield doesn't have.
anyway, to stay on topic, the invisible shield rear skin would be perfect to protect the rear back and sides of the phone, i used to have it on mine, but the seidio innocase II doesn't fit well with it on, so i removed it. if you arent keeping it in a case at all times like i am, i would order the rear shield from one of the reputable skin websites, such as bestskinsever.com, bodyguardz.com, zagg.com and the other places i cannot think of right now.