I like the ones from Power Support - you can get either anti-glare or crystal clear.
POWER SUPPORT
I've tried both finishes (one each on iPhone 3G and iPod Touch). actually on my iPhone I have the Air Jacket set which also includes a very thin plastic case for the back, but the front film is same as what you can buy separately.
because they are slightly stiff compared to some really thin ones I've tried before on my various cameras, the Power Support ones are VERY easy to put on without any bubbles or wrinkles. you can take them off and reapply them easily, if you need. the fit is perfect. took only a couple minutes to put on perfectly.
the clear one is practically invisible and doesn't change the feel of the screen. the matte one has a texture to it, so actually I prefer the clear.
btw I have an Invisible Shield on one of my cameras, and yes it has that sort of rubbery feel - I don't think I'd want that on my iPhone screen.