|Lilith (1964) [Stephen Evshevsky]: Commits suicide (off-screen) by stabbing himself in the chest; his body is shown afterwards when Warren Beatty arrives and finds Kim Hunter beside his body.
Spirits of the Dead (Histoires extraordinaires; Tales of Mystery and Imagination) (1968) [Baron Wilhelm]: Burned to death (off-screen) after Jane Fonda sets fire to the stable.
Easy Rider (1969) [Wyatt 'Captain America']: Shot to death by a redneck in a pickup truck, after Peter turns back to try to help Dennis Hopper; we only see Peter's helmet flying through the air after the shot. (Thanks to Steve and Chevy)
The Hired Hand (1971) [Harry Collings]: Shot by Severn Darden; he manages to shoot Severn in turn, then dies in Warren Oates' arms shortly afterwards.
Dirty Mary Crazy Larry (1974) [Larry]: Killed in a car crash/explosion, along with Susan George and Adam Roarke, when they collide with a train. (Thanks to Chevy)
Open Season (The Recon Game) (1974) [Ken]: Shot to death with a telescopic rifle, along with John Phillip Law and Richard Lynch, by William Holden, after Peter, John and Richard kill Cornelia Sharpe. (Thanks to Stephen)
92 in the Shade (1975) [Tom Skelton]: I have seen two different endings for this film; in one, he is shot to death by Warren Oates in the boat (we only hear the shot over a freeze-frame of Peter's face). In the other version, Peter manages to wrestle the gun away from Warren, and the movie ends with the two of them laughing together.
Futureworld (1976) [Chuck Browning]: Playing a dual role as both the human "Chuck Browning" and his duplicate, the duplicate is destroyed when it falls from a catwalk during a fight with the real "Chuck." ("Chuck" survives the movie.) (Thanks to Stephen)
Nadja (1994) [Dr. Van Helsing/Dracula]: Playing a dual role, "Dracula" is stabbed in the heart with a wooden stake by "Van Helsing."
3:10 to Yuma (2007) [Byron McElroy]: Thrown off of a cliff by Russell Crowe. (Thanks to ND, Mathew, William, and Tommy)