Great thread idea! I wholeheartedly agree with keeping parts on hand. With minimum orders, shipping costs, and difficulty finding some things, it just makes good sense to me. Things I "stockpile" that I consider necessary to keep on hand:
Toroids (T50-2, T80-2, T50-6, T80-6) and some ferrite beads-CWS Bytemark, Toroid King
Caps and resistors - all common values - All, Jameco, Dan's Small Parts & Kits
Transistors - 2N3904, 2N3906, 2N2222, 2N3053, 2N3055 - Jameco, Dan's Small Parts & Kits
FETs and JFETs - 2N3819, MPF102, 2N7000, IRF510 - Jameco, Dan's Small Parts & Kits
Op Amps and Linear - TL074, LM555, LM3900, LM741, LM311 - Jameco, Mouser
Linear Audio Chips - TDA2002 (or 2003), LM386 - Mouser
Regulators - LM7812, LM7806, LM7805, LM7905, LM317, 78L05, 78L06, 78L12 - Jameco, Dan's Small Parts & Kits
MISC: T1.75 LEDs (various colors), 22 ga hookup wire, 20 ga magnet wire, many sizes of heat shrink tubing, RCA connectors, SO239s, 3.5" connectors, 2 and 3 pole terminal blocks, several sizes of potentiometers and trimmers... pant pant pant... whew!
And I'm sure I missed some stuff...
I would imagine everyone has a different list, depending on their main interests...