I purchased a screen protector at Best Buy because it was the only store that wasn't sold out on Black Friday. At first I thought the price was a little high - $24.99 but once the salesperson explained that it came with a lifetime warranty I bought it.
Check out zagg.com for more information. Make sure you follow the installation instructions. You have to keep your kindle turned off for 12 - 24 hours for the screen proctector to adhere properly. I checked mine at 12 hours and there were still some bubbles. After 24 hours the bubbles were gone.
I bought my kids tablets for Christmas (not the Fire) and bought screen protectors for both of them. They have them on their phones and it really helps with the touch screens. If you're going to buy a case, you probably don't need a skin.