Karl Edward Wagner's Kane series (can be hard to find).
And while it's not sword & sorcery, I would recommend Louis L'amours Walking Drum. It's historical fiction, but IMHO, he had a similar writing style to Howard and it fills the "sword" part anyway.
Well, the fantasy elements are a little more... fantastical than REH's works but Fritz Lieber's Farfid and the Grey Mouser books offer some classic swords 'n sorcery action.
And if you don't mind some swords 'n martain princesses then you could try Edgar Rice Burrough's John Carter of Mars. A friend of mine described them as "its like Conan... in space!"
If you don't mind the 1800s or the real world, Bernard Cornwell's Sharpe series is great, bloody, rip-roaring adventure. Not really fantasy, though, heheh.
Don't forget that Robert E. Howard wrote a lot more than just Conan!
Make sure that you check out some of his historical stories...especially those set in the Middle East during the Crusades. Some of these are at least as good as his Conan tales - but are nowhere near as well-known as his fantasy works. The University of Nebraska Press recently published a collection of them under the title Lord of Samarcand and Other Adventure Tales of the Old Orient (ISBN 0-8032-2422-2).
I'd also check out some of the other pulp authors writing around the same time as Howard. Fritz Leiber has already been mentioned, but I'd also check out the works of C.L. Moore, Leigh Brackett, Henry Kuttner, Clark Ashton Smith, Edgar Rice Burroughs, et al.
The good news is that it looks like Paizo will be republishing some of these works as part of the upcoming Planet Stories product line. A couple of them have also recently been reprinted as part of the British Fantasy Masterworks line.
I'd have to second the opinion that Karl Edward Wagner's Kane series is excellent.
Over the years, Howard has spawned a legion of imitators - most of them of fairly mediocre quality. Nonetheless, the works of Lin Carter spring to mind if you're looking for stuff in a similar vein, as do the Kothar and Kyric series by Gardner Fox. These works are long out-of-print, but you can often pick up copies in second-hand boookshops.
If you don't mind the 1800s or the real world, Bernard Cornwell's Sharpe series is great, bloody, rip-roaring adventure. Not really fantasy, though, heheh.
The Heroes of Dark Fantasy site is cool. I've read Conan and the first of the Drus the Legend books. I'll have to check out the other characters. Thanks.