PLE is my go to shop for computer parts. Their prices are very close to the best online prices for most items and they have a really good range in stock.
They are not the kind of place I'd recommend to a non-tech savvy person but if you know what you want they are excellent. To my mind they are geared toward people who have already done the research and don't need to be 'sold' something. If you are less tech savvy you might be better off going to a general consumer store (big brand names, slick sales people etc.)
Their online catalog is an excellent resource and is always up to date and informative