The two that I have used (they are exactly the same skins as far as I can tell except for the guarantee and price) are:
http://www.zagg.com/
and
http://www.bestskinsever.com/servlet/StoreFront
You do have to push harder to get a response and it is not quite as smooth (the stylus). But, as far as I can tell, the two protectors are equal. I get the cheaper one because I don't need a lifetime guarantee. I only keep phones for a couple of years or so (and a lot of people keep them less).