I like Best Skins Ever skins well enough, dunno what the people basing them are basing it on, but I've used them on an iPod touch, iPad, 2 iPod nano's, and an iPod video all with great success. Oh, and a Palm Pre and Palm Pro.
But, I've also used the Monoprice brand screen protectors on my iPads recently and considering the price (<$1 each shipped for iPhone sizes and <$2 for iPad) they're nice enough that I ordered 5 for my wife and my new 4S's. I like that they're cheap enough to buy in bulk and toss of they start to get bubbles or scratches. They have clear and matte for about the same price, and privacy and mirror finished for about $1 or 1.50 more.