We're looking for something clear but somewhat distinctive, fusing traditional styles with the modern toolsets of the iPad/Tablets.
We don't want schlock, but crisp and clean designs that are self-explanatory and intuitive. Icons preferred over words where possible. We value simplicity. This should be something that professional musicians can use for hours a day.
Some random things we like: rounded corners in place of sharp corners (as per the iOS interface), strategically placed shadows (also as per the iOS interface), simple-ish color schemes that are also beautiful (we suspect that white/grey/silver/black/off-white/etc. will be the best color scheme, but we're open to other ideas, especially those that recall certain music publishers).
The background for the music itself should be a simple off-white. No texture.
Remember that the app exists as a means of interacting with the music itself, which should not be dwarfed by the interface itself. The music should take up the most screen space possible.