The enhancement bonus to attack rolls from masterwork weapons is one example. I believe masterwork armor and shields also get a non-magical enhancement bonus to their armor check penalty modifiers.
If I remember correctly, magic weapon and magic fang spells will allow you to overcome DR/magic, but not other forms of damage reduction (such as alignment- or material-based DR). The rules reference for this should be in the spells themselves.
The only non-magical enhancement bonus that comes to mind is the masterwork bonus to hit on weapons all others are magic (to my knowledge, i have often claimed to be always right, but it has never been true)
and it's called MAGIC fang, if they do NOT become magic i think the name is a misnomer.
I can but won't sight an official sorce because it is 2 am an i feel more like going to slee that digging trough the pf books to find a rule that i am positive is right for as i have already said
I AM NEVER WRONG