Ok, think of iTunes 3 pane display. Now, before you chop my head off, hear me out. I think that if the album list could be made to have multiple panes (not just the 3 iTunes has: artist and album and title) it could make the database even more accessible. Using the same strings it uses now, one pane could perhaps display genre, another sort by rating, and yet another sorted by date last played and have the results put in the database window. Sure that can be done now, but I think that a multipane display could make it more "clean". Each pane could have a dropdown box to sort by all the different fields, the proceeding panes would do the same for the results accumulated by the previous pane. So basically I'm suggesting an iTunes like display, but with the configurability of the already existing Album List sorting, and adding as many panes as you want.

http://www.songbirdnest.com/themes/gespaa_...hot_library.png

So, the top two panes could be configured to sort by not only by artist then album, but by any variable fed into it like genre, rating, date last played etc. And it wouldn't have to be limited to that number of panes.

Sidebar + Columns UI + tabs?

You don't even need tabs if you have it in the sidebar, just holding shift gives you a second album list panel. It would be nice if it had its own minimum height setting so you wouldn't need tabs to put it above the playlist either.