There is no official YouTube app but there are a number of good third party apps. In order of ability/functionality:
MegaTube:
- Allows for website navigation
- Search
- Download as…
- Video
- MP3 (downloads as video before converting)
- Upload to YouTube
- Upload to SkyDrive
- History (requires login to your YouTube account)
- Watch Later
Hyper for YouTube:
- Allows for website navigation
- Search
- History (no login required)
- Download as…
- Video
- MP3 (the app user a 3rd party website to convert http://www.video2mp3.net )
MetroTube:
- Search
- Uploads
- Favourites
- Play Later
Andy