Try a Gobie or Blennie or maybe a school of Chromis those are always fun to watch..
1.Yellow Watchman Gobie are favorites
2. From my experience Yellowtail Damsels are pretty non- aggressive unless they are in groups of 3 or less.
3. Black Bar Chromis are cool if you want to order some off of Liveaquaria.
4. Any type of Fariy Wrasse would be a good choice also I like my Redhead Fairy Wrasse. I would stay away from 6 line wrasse as they can bully over time or get aggressive towards new fish you throw in.
As to being Peaceful normally your tank will be peaceful in the order you add your fish. Any fish bigger than what your adding should be added last depending on the size. I've come to notice once your fish establish there homes they can get aggressive. Re-arranging the rock work helps (sometimes). But it's all up to what you want in your tank and what looks nice... HTH