Good question – made me think a bit. Being all about the rig, it's not a question which arises much in this association, though a few members (Arne, for instance) have tried to emphasise the importance of matching the hull to the rig. This was also always emphasised by Tom Colvin, who insisted that the rig and hull had to be designed as a package, or at least matched carefully enough that the best could got from both. His designs could certainly be called 'iconic'. The same is true on this side of the pond of the 'Jonques de Plaisance' of Dmitri LeForestier.
Many of the rest of us tend to put a junk rig on whatever boat we own or have access to at the time. Although this works well, due to the versatility of the rig, few of these have become 'iconic'. The Sunbird 32 comes to mind, along with the various Freedom designs of Gary Hoyt which are near-ideal for conversion, having already been equipped with very robust unstayed masts.
If I had to choose an 'iconic' junk I guess it would be Badger and her sisters from the board of Jay Benford. In the hands of Pete and Annie Hill who built and rigged her, this boat rapidly became a 'junk icon' and did much to popularise the junk rig - and many others have taken this, or a similar path.
I guess my best advice would be to scan the myriad information available on this site, perhaps starting with the 'Boat of the Month' feature. Here you'll find lots of candidates. The following stand out to me:
A fistful of badgers (and a baby) – Zebedee, Ashiki, Hestur, Blue Moon and Elsie N. At least two other members are currently building this design.
A Kingfisher 22 – a design which emerged from Blondie Hasler's collaboration with Kingfisher to produce bone of the first 'production' Western junks.
Tin Hau – David and Lynda Chidell's Colvin-designed 54' steel junk.
Mingming - Roger Taylor's little unsinkable 21' Corribee which has sailed many ocean miles, mostly in the high latitudes of the Arctic.
Malliemac, the sister ship to David Tyler's Tystie – a design emerging from a collaboration between David Tyler and the late David Thomas. David's subsequent award-winning ocean passages in Tystie speak volumes for this as a great blend of rig and hull design.
Your question is very open and invites very subjective responses. Apologies if mine is one such. Finally, though not iconic in the sense of being generally accepted as archetypal, I offer my own subjective choice – Bertie, a genuine replica of Slocum's Spray (if such a thing can exist). In many ways I see this as the closest of Western matches to the type of Chinese vessel for which the rig was developed. Based on a fishing vessel whose working style and location is similar to traditional Chinese fishing it is a similar type: extremely heavy, beamy, shallow draught, with (originally) very low freeboard, bluff bow and stern. One of very few rigs capable of driving such a vessel effectively in all conditions is the junk rig chosen by her owner and builder, Peter Bailey, including a magnificent (and massive) Hong Kong style mainsail of 1,000 sq. ft. If I had to choose a Western junk which best matched the type of vessel on which the rig originated, this would be it.