As all of these responses show, this is a highly personalized question. Pretty much everyone will give you a different answer based on their own likes and dislikes, and on their personal experiences in rocketry. And, these answers will likely change over the course of one's rocketry career. For example, when I got back into rocketry about seven years ago or so, I would have said I really want to recreate not just the rockets I had when I first flew in the seventies, but also the models from the 1973 Estes catalog (that I still have AND got Vern Estes' autograph in at NARAM this year) that I would have bought and built IF I had the money to do so back then. The list is pretty extensive - those that I originally had included the Alpha, BT-55 V2, Birdie, Trident and Mini Bomarc. I still have the last two, which survived all these years AND several moves!
Among those models that I wanted but never got (the full list is too extensive to fully itemize here) include the Skydart, Orbital Transport, X-Ray, Saros, Mars Lander, Mars Snooper and many others.
Now, after seven years, the list has expanded. I've added low power kits like the Big Bertha / Ranger, Sprint, Centuri Firefly, Hummingbird, Saturn V , Saturn 1B, mid power kits like the Maxi Alpha and Maxi Alpha III, and Big Daddy, and even a couple high power kits. ( yeah, it took a while, but the HPR bug did finally bite me - I'm working on the final design for my L1 cert rocket - a 3" tube fin model.
So trust me - a list of must-have models is not only going to differ from rocketeer to rocketeer, but is even a moving target for each person as the go along.:p