From my Shirley Walker wish-list...
It's possible GHOULIES doesn't belong on this list, since the selections included with Intrada's RE-ANIMATOR release are described as everything Band composed specifically for the film. Walker gets joint credit with Band in the actual film, but I've never attempted to analyze all the tracked and reused music to determine how much (if any) original material remains unreleased. In any event, since the Intrada release didn't include an album cover for GHOULIES, I figured I might as well slip it into this thread.
CHICAGO JOE AND THE SHOWGIRL is a phenomenal score, haunting and decadent. Composer interviews suggest Walker wrote all or most of the material on her own, with Zimmer's screen credit being a legal thing. At any rate, they are co-credited in the film itself, and I imagine that's how it would appear on any official album.
Walker's music for Disney's 1997 LOVE BUG reboot, starring Bruce "The Chin" Campbell (not to be confused with the 2005 Linsay Lohan film) is one of my favorite unreleased scores of the nineties. The theme for the villainous car is just spectacular, especially churning out in the low brass during the final race scenes.
As for MYSTERIOUS ISLAND, a single track has been officially released on various Tokyo DisneySea albums. But Walker actually wrote a good deal of material for the various sections of the theme park attraction -- I don't know the exact figure, but it may be as much as 30 or 40 minutes, by some accounts. What I've heard is amazingly powerful stuff, as you'd expect given the composer and subject matter.