Since there are no "Similar" shows listed, I thought I would add some here...
The Rockford Files - He's not a Marlowe clone; far from it. Jim Rockford is the antithesis of the "hard-boiled" PI. He would rather fish than fight, he keeps his gun in a cookie jar, and when there's a fight he's almost always on the losing end of it. But he takes the cases the cops won't touch, and the writing and acting on this show make it one of the best detective shows of all time. James Garner even played Philip Marlowe in 1969's Marlowe, a loose adaptation of Chandler's The Little Sister.
Raines - Jeff Goldblum plays Michael Raines, a Los Angeles homicide detective who has the unusual talent of imagining conversations with the murder victims he is investigating. He struggles with this, and other issues, as he tries to keep his job as a top-notch detective. Unfortunately cancelled after only seven episodes, you can watch for free (as of this date) on NBC.com, or download the series for around $12 at iTunes. Goldblum has said in an interview one of his models for the character of Raines was Elliot Gould's take on Marlowe in Robert Altman's The Long Goodbye, and Raines says he came out to LA because he read too much Raymond Chandler and wanted to write like him.
Nero Wolfe (2001) - Considerably more light-hearted than Marlowe, this show was a period piece adaptation of Rex Stout's Nero Wolfe series. Timothy Hutton and Maury Chaykin starred in a series with consistently high production values and that was very true to the source material.
Happy viewing! Feel free to list any others I might have overlooked.