A question came up in a game last night. Do different types of damage (i.e. cold) have additional effects beyond hp reduction? If so, can someone please give me a reference and page number?
As far as I know, no. Different types of damage don't have additional effects. However, there are various things that grant additional effects such as metamagic and class abilities.
Nope. They might be resisted differently, but there's no additional blistering from Fire damage or anything like that - unless the specific weapon or spell description says so.
They can have additional effects, based on the weaknesses of the target.
For example, a red dragon takes 50% more damage from cold, and a white dragon takes 50% more damage from fire. I don't remember any off the top of my head, but in 3.5 some of the odder monsters might be healed instead (could have been 3rd party things). Negative energy for example, heals undead instead of harming them.
In 3.5, the environment books had rules for environmental effects on spells/abilities based on type (for example, fire was harder to use under water, electrical became area effect under water even if it wasn't before, etc). But I don't think that's been done for PF at this time.
Any additional energy effects would be because of the weaknesses of the creature being attacked, nothing because of the attacker will affect it.
Not necessarily. Any ability the attacker has that increases his fire damage for example would potentially increase his weapon's fire damage. It just depends on how the ability is being gained. For example, if a wizard has a feat that increases any fire spells by N%, then casting 'Flaming Weapon' would increase the damage done by the flaming sword by N%.
Now, having said that, I'm don't actually know of anything in core that allows things like that, but, there's nothing in the rules against feats/class abilities affecting your damage output either (metamagic could boost the damage of a damaging spell, including a spell that burst your blade into flames, and I know there's a spell that does so, sun blade I think it is).