Probably my Star Trek bedding which I'm laying on this very second.
Hmm... Hard to say. I guess my gryffindor robes and/or my small but growing collection of figma figures. Seriously, Japan makes the best hobby products. I have a lot of nerdy posters around my bed too. And my manga shelf. Possibly my complete Sherlock Holmes collection?
I have a lot of nerdy stuff. :)
My complete Stargate DVD collection (SG-1, Atlantis and Universe).
My whole bookshelf is also quite nerdy, it includes everything in the "Dark Tower"-franchise (all books, the concordance and the comics), a couple of astronomy books and several about computer science.
Oh my goodnes, this is difficult, because many of my possessions are incredibly nerdy. But, some top picks:
•I have a pair of earrings shaped like DNA double helices. No joke.
•My Red Blood Cell plushie
•My "Weasley is our King" T-shirt
•A polymer clay figurine of the Eleventh Doctor that I made :) (and various other fictional characters, but the Doctor is my favourite, and possibly the nerdiest)
Probably Darth Vader's TIE Fighter in Lego form. Or the Burrow in Lego form. And my Time Turner.
erumpent horn neckless i made
'butterbeer' cork necklace like Lunas