Long awaited Skype app is launched on marketplace on 2/25/2012. Although its not searchable directly on marketplace at moment, wierd though i managed to find a way to download it from there blog post.
If you want to upload it through Zune, below is the link
Or by opening the same post and click here
And keeping it more simple and utilizing the windows phone 7 you can press the search button and scan for the QR code below