We've got friends who live in the Park Slope section of Brooklyn and I always love walking by the Brooklyn Superhero Supply Co. storefront.
I haven't had a need to go in and buy any antimatter, but the Sidekick Placement Service always looks intriguing.
In fact, the storefront and the website are just promotional fronts for 826NYC, a worthwhile nonprofit organization that provides programs to encourage creative and expository writing among young children in New York.
That said, if you need to pick up some bulletproof tights or capes, this is the place for you. Just be aware: No X-Ray vision use inside, and they request you initiate your interdimentional travel outside the store.