This has been my favourite book store for 10 years now. As their name says, they have seriously weird $h!t.
Where else in Melbourne can you find a shop that offers a colouring book strongly featuring the female anatomy (complete with a set of crayons!), Mexican wrestling masks, and a strong offering of collectible & crazy books.
The Andy Riley books always bring me back for more, and inevitably I have to leave the store VERY quickly because I always buy way more than what I originally intended.

Approximate cost: $20+

Great range of quirky little books, as well as a range of pop-culture related literature and a number of things you can't find in regular stores. Highly recommended

great shop, a very eclectic mix of literature, has been a staple of Brunswick St for many years

Excellent specialty bookstore - great for presents and unusual gifts or specific titles. Good selection and wide variety - always busy, always pushing boundaries.

Approximate cost: $5 - 100

The best bookshop in Brunswick Street. Obscure amazing stuff. Art and music books and magazines etc. the best you can find. Always something very different. Friendly obliging staff. Find books here you would never find anywhere in Australia.

Fun place to browse if you're on Brunswick Street. Lots of interesting novelty books and stuff you won't find on display at Angus & Robertson. If you're looking for something in particular, ask the staff -- you might not find it on the shelves yourself, stock is only vaguely in any kind of order.