CustomSLR's Glide Strap ($35.95 for the strap and $64.95 for a combo with the C-Loop Camera Strap Mount) is a very comfortable, generally well-designed sling strap that's worth the money over the typical cheap neck strap that comes bundled with most cameras.
The highly modular architecture involves several components: a clever neoprene shoulder pad (the Glide Strap with Split Strap technology) with a gap in the middle and quick-release rotating endcaps to better mold itself to your body; 70 inches of slick-textured webbing; a plastic connector that slides along the strap plus a single cam buckle to act as a stop; and a pair of small straps that attach the connector to the C-Loop camera mount.
My favorite part of the system -- the part that I have zero problems with -- is the C-Loop, which has a very clever and attractive design. It stands out overattachment in two notable ways: it has a little handle that makes it easier to screw in (which gives it an edge over design as well) and it's flat-bottomed so that you can more easily perch the camera to stabilize it when shooting video or at slow shutter speeds.
The Split Strap is as comfortable as advertised, and despite some initial reservations about it possibly getting a little grotty-looking over time like other Neoprene products I've used, it seems to be wearing pretty well.