Great list! Some of my favorite supporting roles/actors are; Evil Ed (Stephen Geoffreys) from Fight Night, Trash (Linnea Quigley) from Return of the Living Dead, Mademoiselle (Catherine Begin) from Martyrs, and the hitchhiker (Edwin Neal) from the original Texas Chainsaw Massacre.
Excellent choices, Josh! I almost included Evil Ed on this list. As for Return of the Living Dead, at some point I plan to include it in a “best horror ensembles” list.