Since everybody is turning nostalgic...
There's plently of sets I remember fondly (the 6392 airport being one). I'm lucky enough to still have them, including boxes and manuals, although I can't see myself displaying them (a bit bare for that).
I don't have real regrets about not being able to put my hands on a set, but if there's one, that probably would be this one~:
I'd still be interested in it today, although I've a couple Mindstorm boxes (the first one being the Robotic Inventions box including a RCX offered by friends twelve years ago... I hadn't touch a Lego for years, and a couple days later, my parents were surprised to see me digging them out of storage ^_^ )