Well, hunters need a lot of things too, not only charms, but this post is about charm so I have some ideas.
A charm for Sharpen Senses, it could increase the endurance you get and your maximum endurance for more time, or in it's defect, a charm that let you regain endurance faster, or like the Charm of Energy, one that refunds endurance if an attack fails.
A charm for a pet could be nice too, one that allows you to revive your pet at 75% of it's life.
A charm that increase your walk speed for more time, maybe 50% for 12 seconds.
I also thought about interrupt a cast, but in my opinion it could be a skill instead of charm, as a loner hunter for almost 25 levels, a skill to interrupt a cast would've been very handy.