I just constructed a command that helped me find my lost stash commit:
for ref in `find .git/objects | sed -e 's#.git/objects/##' | grep / | tr -d /`; do if [ `git cat-file -t $ref` = "commit" ]; then git show --summary $ref; fi; done | less
This lists all the objects in the .git/objects tree, locates the ones that are of type commit, then shows a summary of each one. From this point it was just a matter of looking through the commits to find an appropriate "WIP on work: 6a9bb2" ("work" is my branch, 619bb2 is a recent commit).
I note that if I use "git stash apply" instead of "git stash pop" I wouldn't have this problem, and if I use "git stash save message" then the commit might have been easier to find.
Update: With Nathan's idea, this becomes shorter:
for ref in `git fsck --unreachable | grep commit | cut -d'' -f3`; do git show --summary $ref; done | less