I have what my husband calls "music ADD." I don't have it nearly as bad as he does, tho, but that's because he's probably actually ADHD.
It's when I keep switching music. Constantly. Before songs even finish. I'm really just looking for the perfect sound for my mood. And when I'm not really sure what kind of mood I'm in I just don't know what kind of music I want to listen to. Since soundtracks are my favorite genre they usually do the trick, but it still takes a while to find the right one.
Do I want instrumental?
A musical? (Not always the same as showtunes.)
Etc., etc., etc.
I've noticed when I'm in a bad mood I usually turn to louder music, but then I have to decide if I want a male or female voice. I usually pick My Chemical Romance or Garbage.
When I'm in a really good mood I want a musical. Depending on the sub-mood I choose Sound of Music, Moulin Rouge, Mamma Mia!, or one of the classics such as Singing in the Rain. These days a super good mood calls for the Muppet Movie soundtrack.
When I'm in a girly mood (this doesn't happen often) I listen to Alanis, Imogen Heap, Emiliana Torrini, Shawn Colvin, Vanessa Carlton, or T.A.T.u.
For the generic mood there's The Wind or a gazillion different soundtracks to choose from. One of my favorites is 10 Things I Hate About You (I have a thing for 90s soundtracks). Let's just watch the last scene and song: