At 12.5 damage per hit, assuming a longbow, that would imply that you're +8 on the damage rolls from the combination of all factors. That's not bad, but as you get to level 10 or so you can be doing better than that.
A. Weapon Specialization and ranged weapon mastery. This will take four levels of fighter or three levels of pious templar, but that adds +4 damage to the top of what you're doing. If you're willing to put 12 levels into fighter, greater weapon specialization will kick the damage bonus up to +6 per arrow.
If you have cleric or paladin levels and a decent charisma bonus, divine might is a good feat for this purpose too.
B. Belt of Giant strength and a higher strength bow. A lot of archers are hesitant to increase their strength because that would require selling their old strength bow and buying a new one. Suck up the cost and do it now and, in the future you will be glad you did. The 2-3 points of damage from a belt of giant strength is damage you can't get from anywhere else and it will add up quickly.
C. Favored enemy (if you have ranger levels)
D. Buffs. Greater Magic weapon is pretty standard in 3.x D&D. Flame arrow and, situationally, sonic weapon also help a lot. If you are a cleric (which I'm guessing you're not, but you didn't say), quickened divine favor helps a lot.
E. Convince someone to play a bard/get a bard cohort. (or a nobility domain cleric). Some masterwork drums and Inspirational Boost and +3 to hit/+4 damage will see exponential improvements in your party's damage output.
Now that's a separate question from defeating DR. A +1 holy bow is almost certainly your best bet on that department. (A +1 sacred bow, however, is cheaper and works almost as well--if your DM allows them, you could also go for a fiendslayer weapon augment crystal from the MIC). Get a quiver of Ehlonna and fill it with cold iron and silver arrows (and a few adamantine ones too just in case) and you're good to go.
Other possibilities:
Skirmish and favored enemy as others have mentioned.
If you go the Pious Tempar route, Divine Sacrifice.
C. Just crank your ordinary per hit damage up there. In the age of worms game I'm playing right now, our archer has a 20 strength, weapon specialization, greater weapon specialization, and ranged weapon mastery. With the usual +4 greater magic weapon from our favored soul, that's 1d8+15 per hit. If he has to work past DR, it hurts, but he's still dealing noticable damage.
D. Carry a greatsword. Most classes that make good archers also get martial weapon proficiency. And archers should have good strengths every bit as much as melee fighters. So, pack a worthwhile melee weapon and when you can't get the job done with your bow, pull out the greatsword and get swinging. Spending a feat on Power Attack and/or Quickdraw can be very handy in this regard too.
