Lack of official full-fledged YouTube app for Windows Phone devices has led to lots of good 3rd party clients. We had the popular MetroTube YouTube client, and now we have got toib. This app features most of the YouTube related functions which an average user will look for it.
• Login to your YouTube account
• Live Tile support app tile and channels
• Browse YouTube videos
• Search YouTube videos
• Buffer support
Download it here from Windows Phone Store.