These three watches are all iconic in my opinion, but all for different reasons.
The IWC GST Chrono isn't as well known outside of the replica crowd, to be honest, but it's a stunning example of 7750 goodness. The Titanium case is excellent and it has the best designed metal strap of any watch. I was tempted to put the MoonWatch in its place, because it is by far more iconic and it went to the bloody moon; You just can't beat that, but the GST is my personal favourite chrono. I'd buy a gen in a heartbeat if I had the cash.
The Rolex Submariner is ... come on, it's a Sub. This is the latest incarnation of the classic design that launched a thousand wanabees. Think Bond and his Aston Martin, tux and babes.
The Panerai PAM 111h is a perfect example of a classic Panerai. It doesn't look like a tuna can with alphabetti spaghetti on it, and it just isn't trying too hard. This watch is the watch yuo can dress up like a barbie doll in its little straps and buckles, giving you a watch for all occasions, almost.