sort by year, total plays, personal playcount, current popularity, genre, tempo, etc.
On top of that, sorting should be stackable, e.g. sort by album by year, or sort artist by total plays, etc.
This could apply to within the artists' pages as well, allowing us to sort through all their songs to better find music that suits our tastes.
Lastly, this could lend itself to the creation of smart playlists, e.g. a playlist that pulls songs from my collection (or from another playlist) that are within a certain genre and released in a particular year.
iTunes has had these features for many, many years - it's time that Spotify catch up!