A couple of things you can use come to mind. Decorgal has a posebox
here with facial overlays included (you can combine them to get different expressions and using the "neutral" expression in combination with others will make them less exaggerated and cartoonish, if that's what you're after).
There's another overlay hack done by Akihiro, who took Decorgal's sit/stand talk animations and turned them into overlays. It's
here.
I believe, as well, aikea_guinea's paintings have some overlays. They're
here and
here.