IMO no arthropod collection would be complete without a few tailless whip scorpions and vinegaroons. Damon diadema seems to be the most common of the TL whips and they can be found fairly readily. I know at least 1 Canadian breeder who has,or at least had, some of the uber incredible CBB Heterophrynus batesii as well. Very impressive animals. Mastigoproctus giganteus is the most common vinegaroon species available. They are a little less common than the D. diadema but they are available, usually as WC juveniles to adults. Both of these species, D. diadema and M. giganteus are very easy to maintain and are not terribly expensive to acquire or take care of.
Of course you have your millipedes and centipedes which are pretty cool as well. They can be as cheap or as expensive as you want them to be really with some species being harder to get and maintain than others. I just picked up three giant African millipedes (Archispirostreptus gigas) which can be a bit difficult an pricey to obtain here in the states.
I'm considering getting into the wet side of the arthropod family (phylum if we want to be totally accurate) with a few of the many types of crabs or shrimp that are available. I'm in the process now of designing an aquatic setup that will allow me to keep a variety of marine shrimp and crab species in one system that gives me the stability of a large volume of water but still gives the smaller individual tanks for display and for keeping incompatible species separate.
I'm a lot like you, its a fascinating group of animals. Definitely the most interesting by far in my opinion and there is quite a variety available depending on how much you want to diversify your interest. Of course I am basing my info off of U.S. availability, I'm not sure about Canada.
Best of luck to you.
