Considering I can only draw from the experience of a relatively short life (20 years), I can't really say the likes of Colin Bell.
There will always be a couple from by-gone times that stick out in my memory though. The Goat and Nicky Weaver, in my opinion, were the two that brought us back to where we are now and without them we could very well still be lurking in the lower leagues.
If I had to pick one, I would say Nicky Weaver. Simply because he's the player I always wanted to be as a kid. I played in net for my team and I found some of his performances absolutely awe inspiring. It's a shame that he never reached his full potential.
I still remember, quite vividly, us beating Ipswich 1-0 at Maine Road. Nicky put in a performance that, to this day, would be very difficult for any keeper to match. I was nine at the time and to me he appeared to be some kind of goal-keeping god, nobody was going to score past him in my eyes.