Well to tell you the truth, you really don't need a screen cover at all. The Kindle isn't a touch screen so just keep your fingers off of it and you'll be fine.
Cases run the gamut from cheap and practical to -- OMG that cost almost as much as the Kindle itself!
There is an entire forum over at Kindleboards.com dedicated to dressing your Kindle up pretty and people even post pictures of how their Kindles look all decorated. You might want to check that out.