Your favorite niche/specialty/unique stores in DC

Brownie points if you answer in this format: store name, location, what they sell, and why you like it!

I'm planning a trip to DC sometime soon, and aside from museums and monuments, I'd also like to do some window shopping—and actual shopping. I want your top picks for stores that sell or specialize in something fairly niche or specific. It could be literally anything: specialty books, hats, leather goods, contemporary furniture, fountain pens, wristwatches, glass, ceramics, anime figurines, hi-fi equipment, novelty gifts, etc.

Some stores I already have written in my notes: * Fahrney's Pens * Labyrinth Games & Puzzles * Bold Fork Books * Reiter's Books * Smash! Records