Op/Tech USA Super Classic c/w pro-loop & quick disconnects
Camera straps are a notoriously difficult thing to get right. Those bundled with the camera aren't usually comfortable and they stand-out a mile; making you and your camera an easy target for even the most clueless of villains.
ThinkTank Photo make a decent webbing strap, and they even bundle one with the Rotation 360 backpack but while strong and secure, it's not as comfortable over a day.
The most comfortable I've come across and use for all the camera reviews, as well as our own cameras, is the Op/Tech USA Super Classic with pro-loops (for effortless changing between cameras) and quick disconnects.
The latter feature, a pair of Fastex quick-release buckles, takes some getting used to, especially when you have a Canon 1Ds MkIII and suitably expensive L-series lens dangling from it. But for all that, we've never had an accidental spill and they come in handy when you want to remove the neoprene pad, for example, when setting the camera up on a tripod.
I would probably like it more without the disconnects, but even with them the Super Classic is the most comfortable strap I've ever seen, and I've seen plenty.