1. A computer-implemented process, comprising: identifying, by a computer server system, a base topic for a personalized media stream for a user of a computer system; identifying, with the computer server system, a plurality of media items associated with the base topic using a plurality of different and independent categories of media categorization data, wherein each of the categories of media categorization data is assigned a weighting; building a collection of candidate media items from the identified plurality of media items; ordering the collection of candidate media items to form a personalized media stream; and providing the ordered collection of candidate media items for playing to the user, wherein the ordering of the ordered collection depends on particular weightings assigned to corresponding categories of the media categorization data.