Computer parts, Washington?

There are a few Microcenters in and around Washington DC.
They would be a great, great place to start.

Ok, thanks for the help, are there any other ones I should know about?
Got a relative that's going to D.C, but only for a couple of days and he don't know where he will be staying yet, so I want to cover as many stores as I can.  

If you can order from newegg that would be the best choice.

Yeah I know, the problem is that if I order from them I will most likely be charged both tax and customs, which will make it more expensive than if I bought everything here.

Well no, if you receive the items at an address in the US there will be no tax or customs. Not only are the prices and selection better with newegg you wont get charged with sales tax like you would at a normal store.

The thing is that I'm from Europe. But as you have lower prices in the US, I was thinking of taking the chance of getting some stuff cheaper when I had it.

Yeah, I understand. I'm just saying the cheapest and best option would be using newegg while you are in the states if at all possible.