1. A computer-implemented process, comprising: identifying, by a computer server system, a base topic of a personalized media stream; identifying, with the computer server system, a first media item associated with the base topic based on first data from a first source, wherein the first data is assigned a first weighting of the first source, and wherein the first weighting of the first source is based on a first plurality of factors, wherein the first plurality of factors comprises an identified level of familiarity associated with the base topic and an identified level of popularity in another personalized media stream; identifying, with the computer server system, a second media item associated with the base topic based on second data from a second source, wherein the second data is assigned a second weighting of the second source, and wherein the second weighting of the second source is based on a second plurality of factors; building a collection of candidate media items that includes the first and second media items; ordering the collection of candidate media items to form the personalized media stream, wherein ordering the collection includes ordering the first media item within the collection based on the first weighting and ordering the second media item within the collection based on the second weighting; and communicating the personalized media stream to a client device for playback.