Here is a list of various things I track for my own use and reference.
Books (Wiki) - Books I read and finished reading together with a link to the notes I made on each of the books and my reviews.
Books (Trello) - Books I am reading now and planning to read.
Series (Wiki) - TV series I saw already with my thoughts and a small reviews on each one.
Music playlists - Different playlists I made of music I like.
Spotify - Different Spotify playlists I made.
SoundCloud - Different music I liked.
Last.fm - Music I am listening to now and listened to in the past.
WakaTime - Ratio of different programming languages I used this week together with the editors I used.
Games (Wiki) - Games I played and my thoughts on them together with my favorite games of all time.
YouTube playlists - Various YouTube playlists I made.