I never knew how badly I wanted a store like this around, there've been so many times I'm mid-project or rebuild and the old bolt/nut/fastener/whatever either breaks/gets lost/shot and I just have to wait for the part to come in or wade through the bins at a hardware store which have been waded through by everyone else and now I'm frustrated...

Whenever I've gone in, there was always a line at the counter!

I use them for all replacement bolts in my car except for internal engine bolts, where I source them from racing suppliers.

Or, for the online, next-day delivery version of this, McMaster-Carr. For example, here's their catalog for one type of (rather expensive) screw:

http://www.mcmaster.com/#socket-head-cap-screws/=vrc2nx

I love how much information McMaster gives you. Mechanical drawings and 3D CAD models of course, and also descriptions of how things are used, the properties of different materials, how to size stuff, etc. All the basic things you need to know to design something.

McMaster-Carr's fulfillment services are truly top-notch. There have been times that I've specifically ordered from them because I knew that I'd have it the next day. They've never failed to impress me with their service.

Their physical catalog is one hard catalog that I really miss! Despite the fact that the website undoubtedly offers more product than the multi-thousand paged hard edition, I remember many projects in my college days inspired by simply flipping through it's pages.

As a studio art major in another life, I can't recommend McMaster-Carr enough! I was doing a lot of metal fabrication, lighting, and plexiglass work, I can't imagine finishing my thesis without their selection and speed. Not to mention all I learned just by reading their great descriptions and images.