There's the obvious connection: starred Mel Gibson, who starred with Heath in
The Patriot.And the less obvious...also starred Sam Elliott, who was in
Thank You For Smoking, which starred Aaron Eckhart, who plays Harvey Dent in the upcoming
The Dark Knight, with Heath as the Joker. Sam Elliott was also in
Hulk, directed by Ang Lee, who directed
Brokeback Mountain.
Besides that, Sam Elliott has played lots and lots of cowboys in his career.