Books:
...and the Philosopher's Stone (British paperback)
...and the Chamber of Secrets (same as above)
...and the Prisoner of Azkaban (- " -)
...and the Goblet of Fire (American hardcover)
...and the Order of the Phoenix (British hardcover)
...und der Stein der Weisen (German hardcover)
...und die Kammer des Schreckens (same)
...und der Gefangene von Askaban (- " -)
...und der Feuerkelch (- " -)
...und der Orden des Phoenix (- " -)
(I wish there were German paperbacks. I paid 28 Euros for OotP. Luckily there will be only seven books

)
Poster: Harry Potter and the Philosopher's Stone (like
this but without the text and the logo is in the upper right corner)
That's all I own. I used to have Bertie Bott's Every Flavour Beans when the first movie came out, but they tasted awful and it was easy to recognize the "good-tasting" ones ("Harry Potter" was printed on them).
Maybe I'll knit myself a scarf one day. I think Ravenclaw would look good. Or all four.