Gun law had the real characters Matt Dillon and Doc Holliday.
Not historically accurate I suppose.
I read that someone just identified an old photo as showing both Billy the Kid and Pat Garret who later killed him. Worth millions.

Carry On Cowboy mentioned above. Not TV but had a great song.

All my favourites already mentioned, except A Man Called Shenandoah which had a version of Oh Shenandoah written for it. He was played by Robert Horton who also played Flint McCullough, the scout on Wagon Train mentioned above.
There was an Australian "Western" called Whiplash that also had a good song.