As stated, flowerpots are not well known for their longevity in captivity. I put a
Hammer Coral in for my Perc. Took him about 6 weeks to take interest, but when he decided to host the hammer, he dove in with gusto. Not only is the Hammer a good choice for the perc, but it's become my favorite coral. It opens very large, and at times the perc will dive in and be totally obscured, only to come peeking out at another place. I just can't say enough good about the relationship between my percula and hammer. (I really MUST get a digital camera soon)
Some people seem to be keeping anemones with a degree of success, but most of those I have talked to have had them die within a few months. You are wise in not choosing one of these.
Percs have also been known to host
Torch Coral and FrogSpawn.
Good luck,
bobc