1. Get the most recently uploaded videos of any YouTube user
https://gdata.youtube.com/feeds/api/users/<user>/uploads [example]

2. Get the RSS feed of videos that contain a particular tag
https://gdata.youtube.com/feeds/api/videos/-/<tag> [example]

3. Get the RSS feed for any search query on YouTube
https://gdata.youtube.com/feeds/api/videos?q=<query>&orderby=relevance [example]