My definition of creeps is some random units that are hostile to all that can be killed for exp/gold. If we see some of these guys wandering around the map i'd be very happy. I guess wild animals like deer, elf, and bear could be considered creeps also, but these shouldn't be so vicious and act more as a food source.
Also, it would be cool if there were some neutral creeps, like nomads, going around the map and you could trade resources or gold with them. This may solve the mercenary problem and add a new market to increase economic wealth.