Some great names have been meantioned on this thread, brought back many fond memories. For me it's between two - Tommy Hutchinson, the best player I've seen wearing the Sky Blue shirt since 1964, the excitement he generated -fabulous. But to answer the question the most inspired signing was Terry Yorath. Best captain ever lead the team from midfield, got the players playing and comanded upmost respect.
Great thread
I've not gone through all the posts so I may be repeating stuff here, but I think Chippo was inspired. Not only did he help convince Hadji to join, but he was also great for us. But more obvious one has to be McAllister. He was truly class.