Well, you gave an idea with the locks - a character who has an ability to pick locks can be quite nice for the treasure hunting players. Or perhaps to make getting through an area a little easier when you don't have to always find the keys that open the door to the way out.
Really, it often depends on what you have going on your game. Whilst I did download a recent version, I've yet to actually sit down and play it through. But some ideas from the top of my head that you can always make changes in the game to incorporate (these ideas come from an old test project of mine that involved characters that had unique field abilities):
Climb - Having this character lets you climb up certain things such as cracked walls, vines etc to reach higher ground, or go down to lower ground.
Smash/Break - Strong character can break down weakened walls or wooden barriers.
Geomancy - A magic-type character can use the terrain properties that have different effects. Or perhaps rename this to allow a magic user to use certain magic elements in the field: fire to burn things, water to extinguish fires etc.
Scavenge/Search - Searches the area to find items; may find rare items in certain places. May even be able to extend this to find hidden paths etc.
Dig/Unearth - Similar to scavenge, find items underneath hero. Can only be used in certain areas such as deserts or soily ground. Also, like above, may even be able to extend this to find hidden paths etc.
Smooth Talker - Charismatic character that can often get more info from NPCs. Perhaps even obtain items or secret locations.
Those are a few ideas I could think of at the moment.
Often, these kinds of abilities provide the player with additional items, access to new areas or simply makes things a little easier. Sometimes, though, you want want them to solve certain types of puzzles.
You want to be careful, though, that the need for a certain ability to get through a part of the game is made known or an alternative solution provided (like with the locked door idea - you can use a lockpicking character or find a key somewhere) so that players don't have to backtrack to change their character so that they can progress. It'll likely throw them off the game altogether.