I've noticed that some weapons have an affix that states "X.X% chance to inflict Bleed for XXX-XXX damage over 5 seconds". This seems like a cheap way to increase my DPS especially against monsters with a lot of hitpoints, but I tend to use the Barbarian skill "Rend" which also inflicts a Bleed effect. Answers to this question seem to imply that stacking DoTs is not possible for one given ability - however I'm unclear on whether this counts as the same ability since it is a Bleed effect, but from a separate source.
I suspect there must be other similar cases with Poison effects and others which apply to different classes, however I am not aware of specific examples.