Below are some useful links to paladin related threads. If you're interested in learning how to be all you can be, these resources are a good place to start. I give credit to all of the original authors. I'm just spreading the word here. MMO-Champion and Elitist Jerks are generally where I look first when I have questions about how to play any class. Sometimes threads will differ between the two, which I think is a good thing. Doing your own testing and consideration is the mark of a good player.
Between MMO and EJ, you should be able to find the most current opinions on these specs. I may post up my own guide on Ret and Holy, but right now that feels a touch redundant.
Elitist Jerks Prot
Elitist Jerks Ret
Elitist Jerks Holy