John Stark was the hero. I haven't actually read that yet, though I've had the later trilogy (The Ginger Star, The Hounds of Skaith, The Reavers of Skaith) for years - I wanted to read the earlier duo first (The Secret of Sinharat, People of the Talisman) and finally found it awhile ago. The first two were originally from 1949 and 1951 and were set in the solar system and, when she returned to it in the 70s, she reset it outside the solar system, naturally enough.
She was mainly a Planet Stories sort of author who wrote swashbuckling "planetary romance" influenced by Burroughs. She collaborated with Bradbury some, I think. She could also turn her hand to a little more austere space opera. But she's probably best in the planetary romance or weird sort of tale where her lush visual writing style could have full play.
I've probably most enjoyed The Best of Leigh Brackett but I've also read and enjoyed The Sword of Rhiannon (planetary romance), and The Starmen of Llyrdis and The Big Jump (space opera-ish), and also have The Nemesis from Terra to read.
She was also married to the SF author Edmond Hamilton.
-- Oh yeah: I think her most famous single work is probably The Long Tomorrow. I haven't had any interest in that since it's supposed to be a pared-down post-apocalyptic novel and I don't generally care for those, but it's well regarded.
Oh, and of course, she's written the screenplays to many films, usually famous westerns, but is credited with the initial take on The Empire Strikes Back, though she died just before it was done.
Huh. Maybe there's even more she's done, since I keep thinking of stuff, but I think those are the main highlights.