There are many audio editing software that allow loop markers to be saved. This information is saved in the .wav info chink, and will be readable by various other pieces of software or hardware samplers. On OSX, Bias Peak is one I know has this function. I'm not aware of any free audio editors that have the capacity to export loop markers.
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I would go so far as to call it the SoundForge of Mac OS. It's also very reasonably priced (Loop Editor $49.99, and Wave Editor on sale currently at $69.99), and you can download a 15-day full featured demo I believe. I also couldn't live without their Sample Manager software. All of them handle audio file markers -- Wave Editor can add loops points too, but Loop Editor gives some extra functionality that comes in handy, like a zero-cross view.
Don't forget the new major player on the mac - adobe audition, once known as cooledit/coolpro.
Support and implementation for these markers and how they are interpreted varies from software to software and if you're working with an SDK that too would be specific about the kind of markers it expects to see. I think that's as much standardised as these things get........ :/ Definitely check out the trial versions before you commit to a specific product.