Tailoring (bags/thread), leatherworking (armor kits/leg armor), alchemy, enchanting, jewelcrafting: you can get (most) everything you could want from others that have that particular profession. Blacksmithing and Engineering on the other hand have some very good items that can only be used by the maker. Engineering has the goggles, various toys, and the nifty helicopter mounts. Blacksmithing has epic chest pieces for DPS (if armorsmith), the BoE boot pattern that drops in SSC/TK (boots are BoP), epic weapons (if the particular weaponsmith).
Given your current professions it would be easiest to drop skinning for jewelcrating, engineering, or blacksmithing, or drop either one to pick up enchanting. That way you have the gathering skill to match your crafting skill, unless you plan to just buy everything off the AH, then it really doesn't matter.
Just pick what you feel gives you the best items for your Paladin and go with that.