My favorite tag editor is Mp3tag and I use it at least a couple times a week to populate the album artist field that both WMP and Zune seem to depend upon for proper organization.  Instead of manually typing in each album artist field I use this handy script:

$if(%band%,%band%,%artist%)

Basically if the album artist field is already populated then I don’t touch it, otherwise I transfer the value from the artist field into the album artist field.  Mp3tag calls the album artist field ‘band’ but I don’t let that stop me.  If you feel like using it as well here is how to add a new action:

1. On the menu select Actions –> Actions (or just hit Alt + 5)
2. Click the ‘New’ icon in the upper right
3. Give the action a name, I used ‘Populate Album Artist’
4. Click the ‘New’ icon again to add an action type
5. Select the ‘Format value’ action type
6. For field select ‘ALBUMARTIST’
7. For format string use: $if(%band%,%band%,%artist%)
8. You’ll end up with a dialog that looks like this:

OK your way through everything and now you have an action to automatically fill out that needed Album Artist field and help prevent the silly ‘Unknown Artist’ folder that Zune seems to like to create.

To use the action it’s as simple as selecting the tracks you’d like to apply it to and then either bringing up the Actions menu from the menu bar or the toolbar icon.

UPDATE: Thanks Oscar for pointing out that you need to remove the space before the %artist% portion of the formula.  I’ve updated the post to reflect that (still working on the screen cap though).

UPDATE #2: I’ve updated the steps to reflect version 2.48 of Mp3tag, this post was a little crusty.  Thanks to Eric Nemchik for pointing out that ALBUMARTIST is now the correct Field vs. BAND in old versions.