I'm taking iconic to mean just that, as opposed to 'my favourite' or the ones I think were the best sets. Though I'll admit I am a little biased towards the ones from my youth, which I think was Lego's golden age (mid 70s to mid 80s). I'm not much of a fan of licensed themes or minifigs either to be honest. I guess younger folk would have less issues with licensed themes, it's the age we live in after all... but they're not really for me.
Weirdly I have nothing from the 80s in there, but I still think of Technic, Space and Town stuff to be more typically '80s' Lego than 70s, or at least that was when I was exposed to it.
So in order of release.... (yes, I have way too much time on my hands, but hey...it's Sunday haha).
3 Basic set (1973)
I think these 70s Basic sets are just classic Lego and really cemented it as a hugely popular toy. Every kid I knew had one of these sets in the late 70s. I'm picking 3 because it was my first big Lego set, but I think they're all great. Give a young child one of these sets today I'd bet they'd still get endless enjoyment from it.
390 1913 Cadillac (1975)
These old Hobby range vintage cars were the biz when I was very young, though a bit before my time. This was big boys Lego and maybe even Lego's first attempt at attracting older fans. I think they still have a great charm and look great on display.
853 Car Chassis (1977)
Arguably not even the best Technic car, but I think this was a big set for Lego, and the flagship of the first Technic range. Lots of people my age would have drooled over this set as kids. I vaguely remember a Lego TV commercial at the time in which this would make a brief appearance, and I would almost crap myself when it came on. A bit before my time again, I ended up getting 8860 which was also great.
600 Police Car (1978)
The first appearance of the iconic minifigure which we all love (or in my case hate haha. I never liked minifigs, even as a kid). I suppose the whole Lego Town range which followed was pretty iconic really.
497 Galaxy Explorer (1979)
The boss of the Classic Space range and starting to fetch mad prices these days. I wasn't really a huge Space fan as a kid but got a few smaller sets for the cool pieces. I mostly used it to try make crappy Millennium Falcons and X-Wings, as did a lot of kids at the time I suspect.
5571 Giant Truck (1996)
I think these Model Team sets were great, the most realistic Lego sets up to that point. The 90s and 00s were Lego free decades for me, but I would have loved this set as kid.
10030 Imperial Star Destroyer (2002)
Gotta have at least one Star Wars set in there and I think this one got a lot of older people back into Lego. Probably the only licensed theme I have any time for. If Lego Star Wars had been around in the early 80s, I may never have left the house.
10182 Cafe Corner (2007)
I don't know how anyone who likes Lego could not like the modulars, and I see these as being future classics. Cool building techniques, they look great and fun for all ages. Lots of Lego win in these.
10220 VW T1 Camper Van (2008)
I think this has been a very popular set and even people not into Lego think it's cool. I was torn between this and the Taj, but I'm putting this in as it's the first set I'd built in 30 years. It's an iconic vehicle and I think will be an iconic set in years to come.
21050 Studio Architecture (2013)
Lego getting back to what it does best and a surprise hit which I think resonated with a lot a lot of older people like me. No licensed theme or exclusive minifigs... just proper, old-skool Lego which encouraged people to use their imagination (which is what Lego used to be all about). It reminds me of the old 70s Basic sets, which kinda brings me full circle.
I think this one will become a bit of a cult classic in years to come, as will the other big Architecture sets. I wish it had been released in Europe too, but if anything it will just add to its cultish desirability, especially for us Europeans.