Comments:
I haven't given particular thought to this question....
But just off the top of my head - Reverso, JLC MMR, Piaget EC, and definitely some from VC........
I‘m currently thinking about adding a Czapek Antarctique Revelation to my collection.
Loved the Czapek Rattrapante already, but that one is too big for my wrist. Other than those two, I think AP is doing a great job on their openworked royal oaks. And FP Journe also did a few nice (semi-)openworked pieces.
Not exactly skeletons but close:
GIRARD-PERREGAUX TOURBILLON WITH THREE GOLD BRIDGES
and
DE Bethune DB28
and
DE Bethune DB28
Skeleton and... skeleton
There are skeletonized watches where people would take a normal movement and remove as much material as they can but the movement has never been conceived to end up like that. End result often look a bit weird.
On the other hand, when a movement had been thought from the beginning to be visually as light as possible, this could be quite an impressive result. Although the less material there is the more your hairy wrist appears as a dial...
My all-time favorite could be the golden bridge. Classical but also the modern versions.
Among the latest production I was impressed by the V Halter résonance where even the wheels seem to have been thought with minimum material. Titanium and germai silver surely helps ensuring rigidity with thinner parts.