The second volume of Del Rey's definative collection of Robert E. Howard's Conan stories contains three of the best ones, The People of the Black Circle, The Hour of the Dragon, and A Witch Shall Be Born.
The People of the Black Circle: Its obvious early on that Howard was really starting to hit his stride with the character by the time he wrote this . It was, at the time, the longest Conan story he ever wrote, and contains multiple plotlines which converge. It also contains some great black humor which would be right at home in today's cinema. My favorite line is, "I think I'll have your heart, Kerim Shah!", at which point the evil wizard telekenetically rips the heart out from the victim's chest. This is basically an oriental adventure story. The geographical names are changed just enough so that the reader will immediately identify with its historical counterpart. India is Vendya, etc. Many people consider this the finest Conan story that REH ever wrote. While its not my personal favorite, its definately in the top five.
The Hour of the Dragon: The only full length Conan novel that Howard ever wrote. Yes, while its true that certain plot elements are derivative of earlier Conan stories (particarly "The Scarlet Citadel" and "Black Colossus"), this is nevertheless a remarkable achievement, and one of the best fantasy adventure novels of all time. Chronologically, its the last Conan story in the saga. Here we have a Conan that is less reckless, and more mature and responsible than his younger counterpart. After he loses his kingdom, he's driven to regain it, not for personal wealth and glory, but to bring justice back to the land on behalf of his subjects. King Conan is depicted as a wise and just ruler craves peace and prosperity, rather than war and conquest, for his kingdom. As its noted in the essay inside the book, whoever renamed this "Conan the Conqueror" missed the point entirely. Don't be fooled though. There's plenty of slaying for even the most die-hard REH fanatic. Let's just say that Conan doesn't kill anyone who doesn't have it coming to them.
A Witch Shall Be Born: Basically, the story itself is pretty forgettable. What makes this story stand out is the one scene that everyone remembers, which is Conan being crucified (this scene was depicted on film very faithfully in the first Conan movie). Was Howard, perhaps on a subconsious level, expressing his views on Christianity? Its an interesting thought. Conan, even after being crucified, is not one to "turn the other cheek". As you'll see, he remains defiant even in the face of certain defeat.
I can't wait for the third and final volume to come out, "The Conquering Sword of Conan".