Bryce, here are my suggestions/opinions/whatnot.
Colombian boas. I don't think you can go wrong with these super popular pets. They're great snakes! Get yourself a super nice pair from a well known breeder and enjoy!
Suri's and BRB's will always be popular. They are super nice looking. Good lookers will always be popular. They take a while to grow up, but then that's all boids. It's hard to produce a bad looking BRB, but choose your suri breeders wisely.
Amazon tree boas. I've got a pair myself, not looking to breed them for anything, but to get myself a real red one, and raise that one as a tame personal pet. As Tim I believe noted, prices are falling. The reason for this, I'm not sure. It's not like they are especially easy, but I guess compared to the ETB's they are. There is a bit of a tree boa following, and it's possible to cater to these folk, however, ATB's due to their aggressive nature will not be as popular as the above boas.
Now for carept pythons. I don't think you can really go wrong with carpets. They're great beginner snake, and come in attractive colours and patterns. Nor do they have difficult husbandary or breeding requirements. Carpets are a particularly popular python, not as much as say balls, but up there.
Bloods/borneos/blacks. My personal opinion is that if you can't get as good reds and blacks as Grant Vg's, don't breed them, but I have an elitist view of these guys, plus Grant's, my pal and I gotta root for him. That being said, bloods/borneos/bloods appear to be on the rise in terms of popularity. Husbandary is more difficult than average snakes, but not terribly so, they get big, but not unbelievably so. I think they're a good choice to get.
Ringed pythons. I don't think these will ever be popular. They have a small following, they're interesting little snakes, but that whole, bright orange disappearing after six months thing is a real turn off.
White lips. The availability of these pythons in Canada is a bit of an annoyance, however, they can be found, with a bit of a price. They're a fantastic python, that I am so glad to be working with, but they're more special needs than most, and have finicky breeding requirements. Plus they take such a long time to grow to maturity, that they're not especially great "investment" snakes, but a snake that you get because you really like them.
There, that's my speel, hopefully, it's helped a bit. I fancy myself a snake market watcher, but I am not infalliable. Whatever you end up choosing, enjoy!