I have two.
Allow Use of Album Artist for the Browser
Maybe I'm old-schooled, but I like being able to use the browser to select artists, genres, and albums. The new iTunes allows the use of Album Artist, but in the Browser, it's still Artist, so I see at the top of my list:
Alicia Keys
Alicia Keys feat. ___
Alicia Keys feat. ___
Alicia Keys feat. ___
...
That's annoying. I would like to be able to switch out this field with things like Album Artist or Composer, etc.
Better Fields for Music OTHER than Modern Songs
Classical has to be horribly mangled genre ever in iTunes. Either the song names have to be horrendously long, or the albums have to be broken out by the peice, rather than by the CD it came from.
A song name should not either have to be Violin Concerto in B-flat minor, Op. 45, I. Allegro. You can't even see that on the iPod. Granted, there's not much meaning in I. Allegro and III. Moderato either, but it'd be nice to have some sort of system to organize the genre. Maybe allow groupings to be as prominent as the other fields, so that we can use it properly in browsing and viewing.