Note: Suppliers marked with an asterisk (*) have a local store for in-person shopping.
McMaster-Carr
Grainger Industrial Supply
MSC Industrial Supply
*Fastenal
*Lowes
*Home Depot
*(Harry's) Ace Hardware
*Craftsman (Sears)
*Harbor Freight Tools
Freret Hardware
Newark/element14
Jameco
DigiKey
Mouser Electronics
All Electronics
SparkFun Electronics
Adafruit Industries
*Radio Shack
MakerShed
MAKE
O'Reilly Books
Instructables
Thingiverse
GrabCAD
Codecademy
DesignSpark
Laitram Machine Shop
IDIYA