An Idea--Reviews, Comments, Suggestions

Another question/issue to add to my list. How can I provide visitors to our web sites a way to offer comments or suggestions (the good old suggestion box idea)? I'm sure there are other parts of our large library system that are doing this, so I'll have to do a little more exploration, but wouldn't it make sense for folks to give us feedback? Or do we rely on e-mail links to do that for us, without a more formal invitation to participate in improving our services, look, feel, etc.?