I only recently became an HP freak, so my collection is pretty small. Here goes:
All movies
Tons of posters (I actually got my local cinema to give me 2 of its promo posters for HBP!!!)
Tales of Beedle the Bard
A witch's uniform
A Gryffindor uniform
A Ravenclaw uniform
A wand
Movie Ticket stubs
A Timeturner
A HP and PS t-shirt
... and that's all. i'm so JEALOUS of BrunhildMalfoy and x.shell.x! I actually write a lot of fan fics and I draw the characters a lot, ao everyone around me knows I'm a HP freak!!