For those mad anime fans we have Shin Tokyo, Lower Ground Floor Rundle Mall Plaza, run by stellar staff with a large selection of pop culture plushies. Build your own Gundams. Large anime and foreign film section with some lovely statues, and all the manga you can read. Keep in mind japan reads books back to front.
For those more interested in Western pop culture, we have Adelaide Comic Centre, 6 Gays Arcade just off Adelaide Arcade, with book shelves stacked with comics from weekly single issues to volumes and even tomes from Marvel, DC, Dark Horse, Image comics and more; and if you don't see it there, feel free to ask their friendly staff to order it in.
They are very customer focused and always make you feel loved and welcome.
Additionally, if you need a gift or been watching these superhero movies lately and wanting to get into the written illustrated works and not sure where to start; they'll point you in the right direction.
For the mad collectors of fine statues, figurines and pop culture paraphernalia you'll find no better than Mad Zombie Collectables, at Shop 1-3 Twin Plaza 22-24 Twin Street. Or right outside from Adelaide Comic Centre!