I would sound a note of caution after the last post. Whilst it may not be an absolute necessity to visit a unit if you can demonstrate previous interest in aviation and a knowledge of ATC through other means, I think it remains pretty important to visit a unit if you are new to this sort of thing. How do you know you want to do this if you have no idea what it's like in a tower?
As for needing a list, use your initiative. Phone the airport switchboard. Ask to be put through to the ATC manager. It's not rocket science.