Most likely a type of tube worm, although it is hard to say. Other options would be barnacles (although doesn't really look like it) or hydroids. Have they moved position at all?
I have those critters in my tank and they don't harm anybody. They also don't multiply out of control. I'd say "keepers". I even like them. I think some kind of tube worm or hydroid too. No barnacles (at least nowhere close to what I got at Radio Island).
The pictures dont do justice to how they look. They look neat as far as asthetics go, and Im sure they arent harming anything and are probaly harnless/beneficial filter feeders. I just wanted to get a positive id on them if possible. Ill go with tubeworm/featherduster type critter for now.