I've walked by this place a millon times (I live less than a block away) but never went in until recently.
I was looking for something really obscure that I couldn't find anywhere else in the city - White Truffle Salt.
Yes, they had it. I took a look around and they have what seems like an endless selection of spices, salts, and other things like fine oils and vinegars. They have more selection than Whole Foods, and way more than the spice store in Kensington, although a bit pricier.
If you are looking for something specific then this is the place to go.
Also, the customer service is beyond excellent. Every person I have interacted with there is very nice, but more importantly, they are very knowledgable and willing to share their knowledge freely and without any of the attitude you can sometimes encounter in other foodie stores.
Highly recommend!