Tokyo Anime Center in Akihabara, a facility created to promote Japanese anime, is holding the Steins;Gate section on the opposite side of the YuruYuri section in their anime exhibition. They display the posters, videos, production materials, and a ton of merchandise of the series as well.
Another entrance (temporarily closed for power saving)
The Steins;Gate section
A poster with the VA's autographs
Production materials - Hand drawing storyboards
Scripts with the VA's autographs
Summer Comiket-limited shopper
Of course they are selling Dr.Pepper!
We can find other anime series' stuff, too.
Panty & Stocking with Garterbelt