Since you're in the US, checkout jameco.com, and have them send their catalog.
It's a small catalog but contains 95% of what I need to build small projects. They
have Arduinos too.
The bigger "industrial-strength" electronics suppliers are digikey.com and mouser.com,
and their catalogs each weigh about 6- or 8-pounds. They handle oodles more stuff than
jameco, but are probably not the best place for ordering parts in 1-seys and 2-seys.