There are a few Pandora apps in the works by 3rd parties and we have our hands on one of them that's just wrapping up beta testing: Radio Controlled by Bushwood Studios.
Based off of the MetroPandora SDK by Justin Angel, which was recently updated to fix the broken APIs, the app has some very nice polish to it--great graphics, fast loading and a unique use of a giant Live Tile within the app for artist/song info. With the updated SDK, you no longer have to re-enter your login information every time you start the app and station selection works much better now.
Radio Controlled features a Live Tile which displays the latest song/album art right on your Start screen and over all gets the job done. The app will be free (ad-supported) and should be in the Marketplace sometime next week--don't worry, we'll let you know when it's live. Overall though you can see devs starting to do some real creative things with the Pandora SDK, resulting in a better selection for everyone. We're pretty excited to have this all going down.