In my 29, I have a percula clown, bicolor blenny, yellowfin fairy wrasse (which I traded my sixline wrasse in for) and a scooter blenny that eats prepared foods. With them, there is a variety of "swimming" patterns...
The clown "wiggles" around everywhere in the tank, the blenny will perch in his hole or on the rocks, swimming around occassionally kissing the glass and rocks for algae, the fairy wrasse will hover around the middle and then dart quickly around the back, and the scooter blenny will scoot around along the bottom or "hang glide" around the rocks and glass.
I loved my sixline and hated it that I decided to trade him in.
I happened to fall in love with the fairy wrasse... saw something a deep, bright pink with lime green top fins and HAD to have it! It's a GORGEOUS fish, but started to nip at my blenny, which is my absolute favorite fish, and I was going to take it back to the LFS until it was "discovered" that my blenny was mistaking my fairy wrasse for a cleaner wrasse!
Like reefkprz said, they are very nice and beneficial to have. I remember getting a tiny colony of zoas and after dipping them and putting them into my tank, out crawled some type of worm looking thing and my sixline, from across the other side of the tank, saw it and dove right it and ate it!