Robert E Howard wrote short stories in many genres, including westerns, fantasy and adventure. Many of his stories were written for pulp magazines, and his westerns ranged from humorous to hardcore. Several of them were published after his death in 1936, and include:

Breckinridge Elkins Stories

These stories featured a kind and strong, but slightly dim-witted cowboy.

1934 A Gent from Bear Creek, Guns of the Mountain, Mountain Man, The Road to Bear Creek & The Scalp Hunter
1935 The Apache Mountain War, Cupid from Bear Creek, The Feud Buster, The Haunted Mountain, The Riot at Cougar Paw & War on Bear Creek
1936 The Conquerin’ Hero of the Humbolts, No Cowherders Wanted, The Curly Wolf of Sawtooth, Evil Deeds at Red Cougar, High Horse Rampage, Pilgrims to the Pecos & Pistol Politics
1937 Sharp’s Gun Serenade
1967 Mayhem and Taxes & Striped Shirts and Busted Hearts
1968 Meet Cap’n Kidd
1971 When Bear Creek Came to Chawed Ear

Pike Bearfield Stories

1936 A Gent from the Pecos, Gents on the Lynch & The Riot at Bucksnort
1956 While Smoke Rolled
1983 The Diablos Trail

Grizzly Elkins Stories

1974 Law-Shooters of Cowtown
1978 Gunman’s Debt

Bucknor Jeopardy Grimes

1936 A Man-Eating Jeopard
1937 Knife River Prodigal
1944 Texas John Alden

The Sonora Kid Stories

1965 Knife, Bullet & Noose
1975 The Devil’s Joker
1988 Brotherly Advice, Desert Rendezvous, Red Curls and Bobbed Hair, The Sonora Kid – Cowhand, The Sonora Kid’s Winning Hand & The West Tower

There were several other Sonora Kid stories published as excerpts in magazines without a title.

Other Western Stories 

1922 Golden Hope Christmas
1928 Drums of the Sunset
1935 Boot-Hill Payoff
1936 Vulture’s Sanctuary & The Vultures of Whapeton
1970 The Extermination of Yellow Donory
1973 Showdown at Hell’s Canyon
1991 Bill Smalley and the Power of the Human Eye