I've been using Rhythmbox to play music, and in it you have a play queue in addition to being able to play directly from the library. It conveniently tells you

I've been using Rhythmbox to play music, and in it you have a play queue in addition to being able to play directly from the library. It conveniently tells you how long total time in the play queue is. I often toss an album in there, then trim it to the amount of time I have before I want to stand up. There's usually a track or two that could stand to be removed. I like energetic music for things that are mostly implementation and little thought (e.g. Dragonforce). While I use more relaxed, less vocal music for things that are mostly planning and thinking (e.g. cello concertos or Mogwai)