This is not necessarily a skill but anyways...
I think it would be cool if crafter classes could choose a 'trait' such as logger, fisher, miner, or creator where they would get a small experience boost from performing an action related to that trait. I am not sure if fishing grants xp in the first place, but if it does fishing can grant a percentage of the base xp gained from it. Since mining grants .15 xp per stone, it can grant an extra .02 xp. Logging down one log brings about 1.5 xp by default, but if that was a crafters trait, they would gain an extra .2 xp. And for creator (which is crafting, I decided to change the name for the sake of not liking repetitive names) they would gain 5% xp from creating items that grant xp in the first place.
Traits for PvP classes could be...
Fast (gives a very small, barely noticeable base speed bonus)
Strong (a moderate increase to damage dealt, maybe .5 extra hit points)
Tough (increased health, maybe by 3-5%)
Intelligent (small boost to mana)