bonsai is awesome, and you can do amazing things with some trees/shrubs that you might not think of immediately (e.g. azaleas, rosemary). my dad was heavily into bonsai for a while and that's how i developed an interest in it. we traveled to nurseries up and down the west coast looking for exceptional trees and also dug up a few promising ones straight out of the ground occasionally. i remember when we found some 5-needle pines out in a forest and being all excited about it.
i love the root over rock style, although it takes a lot of time and patience to get everything to grow correctly and get the roots exposed right without killing the tree. i learned about all sorts of random horticultural stuff during that phase - root pruning, grafting, etc.
our deck was full of bonsai trees - various pines, junipers, maples, elm, boxwood, crabapple, wisteria... the list goes on. i like the grove style as well (what people are calling 'forest' in here) and i also think some cascades are really cool. i was also kind of a bark nerd and still think flaky, gnarly bark on a hundred year old tree that's like 18" high is really impressive. same thing with strong, fat trunks.
jins are also awesome although i could never get the technique right.
the shimpaku (juniper) is a total classic and probably my all-time favorite tree:
(nice bleaching on that one too

)
sick trunk here, i think this is a trident maple (also a classic!) and check out how shallow the pot/root system is:
bonsai is an incredible art form and almost limitless. as long as you don't pronounce it "banzai" you're cool in my book.