Does anyone know where i should go to buy Harry potter posters? Please don't suggest websites.Oh and Harry potter wallpaper?

They usually have them at Wallmart (if you live in America) if not there, probably Hot Topic and Wallgreens. Best buy? Bed bath and beyond? The Wizarding World of Harry Potter?

when it gets closer to the release of Deathly Hallows Walmart will definitely have some. Also F.Y.E. usually has a good variety of them

Suncoast shops are a good bet if they're still around. Also if you're ever at Universal Studios Hollywood, there's a sci fi shop on City Walk that tends to have good film merch as well as several other shops on the block. However, even though you said to not suggest a website, the ultimate best way to get HP posters and cheaply too is through Amazon. I got my amazing Hermione Half Blood Prince poster for $11 and that included shipping and taxes :)

A good place would be Hot Topic, Spencer's Gifts or music stores. Some music stores have posters but not all.

toy r us
they have tons