I really like the idea of creating an Octopart parts list containing most of the common parts used in Arduino projects. I checked out the list made by Kuk but I couldn't find a way to add to it. What I did was create another parts list that includes all of the parts used for the projects in "Making Things Talk" by Tom Igoe. I made the list in such a way that all of the parts can be purchased at once from Digikey (so that someone doesn't have to purchase the parts from several vendors just to get started). Most of the parts have a datasheet associated with them as well.
Octopart doesn't seem to have a way to collaborate on a parts list so maybe Kuk can add the relevant items from my list to the official one?
My list is at http://octopart.com/partlist/view?id=NDQ0MzMz
The list includes 1/4W Resistors at 100, 220, 470, 1k, 10k, 22k, 100k and 1M; Caps at .1uF, 1uF, 10uF and 100uF; 3.3V and 5V TO-220 regulators, Red and Green LEDS, a 2n2222, 1n4004 and a zener diode, TIP120 in a TO-220, reset switches, male header pins and a 9V battery clip. It doesn't include a breadboard, wire or pots (I haven't found a good bread-board mountable pot I like at Digikey yet - I really like the Bourns 3386T-1-104). I began commenting the parts, but I haven't finished that yet.
Hope this helps!