Sometimes in postprocessing, you notice that an image could use some additional texture. Here's a good way to get it:
I keep a compact camera with a decent resolution with me all the time. Any time I see an interesting texture, I capture a quick macro shot of it and save it for a rainy day. I can import it later into a job and blend it into an image, giving it just the right smooth, pebbly, leafy, or any other kind of texture. But what if you don't have the time to go out and find the exact texture you need? Two of my favorite texture sites are Texture King and Bashocorp (both are Royalty Free). They have a nice variety of textures that you can use in any project personal or professional.