EDIT: Check out my newer, more accurate Red Oak here
I'm never satisfied with my wood shaders. I happened to be sitting on my floor, and started looking really closely at the oak floorboards, when I realized my previous wood shaders weren't cutting it. I also researched how real oak looks up close, and I've attempted to duplicate it somewhat. This is different from my previous shaders in that it's more "physically based." I learned that oak wood grain is actually like little tubes, and you can actually blow compressed air through it, so the grain here is modeled after that. Also the little lines running through aren't just lines, but they come from rays radiating out of the center line of the wood. It didn't quite come out as I hoped, but overall the effect is reasonably close to the look of red oak. Hope you like it!
Material ball is from JC Levet (although I modified the scene to remove stuff that is out of camera): http://www.blendswap.com/blends/materials/galvanized-steel-shader/