Mario - why not go with a pygmy angel (cherub or flame - several club members have had success with those and reefs). Or how about shark-nosed goby (like a neon, but has bright yellow on its head) - its a cleaner too, but eats regular food. There are many fang blennies that are gorgeous - because they are so different from your sailfin, they should get along fine. Firefish are interesting and stay on the smaller side - they come in a couple of different colors. Clown gobies are fun and interesting - green, yellow, black, bown, citron... lots of varieties and onlt get 1.5 to 2" long. Fairy wrasses are a good choice - don't get too big and come in a rainbow of colors (and don't have some of the specialized dietary needs of the sand burying varieties (leopard, tamarin, halichoeres, etc.)) - but as noted previosly, many wrasses and other fish, like the firefish, are good jumpers - you'd need to add a lid or put a screen on your tank. Just some suggestions...
You might want to check out Amazon or other online booksellers (maybe even eBay) and look for used copies of any of the Scott W. Michael books (there are several - like "reef aquarium fishes") on marine aquarium fishes. I find they have a lot of good info, good pictures, etc. They are a great resource! (and just to be clear, I do not know Mr. Michael or work for him or anything - I just really love his books!)
