He likes all of the plants, driftwood, rocks and caves for sure. I have one indian almond leaf in there now, I could add a couple more. Outside of those I'm not sure what leaves would be brown... Ideas?
Here's a thread documenting my tank's progress: http://www.monsterfishkeepers.com/forums/threads/my-discus-journey.648726/ Even if it's not this tank, I hope you get a chance to try discus down the line, it took me a while to get up the nerve to do it, but I'm so glad I did. They are easily the most rewarding fish I've ever owned.
Oak is a safe choice as that is what most people seem to be using. I have some drying out right now, but they are not turning brown (at least not yet). I'll stockpile a bunch this fall.