i could imagine rangers and mebbe tigers being able to set up traps. Set up a
trap and wait for the mob to track in the room or the player to walk in etc.

Traps could do a range of things.
damage, the obvious one
snare, think mudpit
hinder, -stats, slice tendons or hit on the head
stun,
or just trigger certain spells targetted at the one who steps in

They could also be of a range, simple things which trigger on the next one who
steps into them, or more compelx thigns who trigger on the next member of
certain race to step on it.

The balancing wouldn't be too hard, just make the traps work like you want
them to, and the most complex traps might require the presence of the trapper
to set them off etc.

Excellent ideas!

To pave the way for thieves, we could also have \"noisemaker\" traps,
which can dropped to a room to alert you whenever someone would approach,
think reaver

This could also be an additional business to merchants, making
chestable traps. So, some traps would have to be made in the room by a ranger,
others could be made beforehand and some of these also by merchs (for example
the counter-thief traps).

Ok, I know thieves are a sensitive subject, but traps could be one element
which could ease their introduction. And even without thieves, traps should be
seriously considered because every respectable fantasy world should have them