The always-inspiring folks at Oomlout are now showing off a forthcoming Arduino breadboard kit they’re working on, a make-your-own ‘Dunio built around the ATMega168 chip. The kit will come with the chip, a breadboard, a hook-up wire kit, and all of the support components you need to wire up a working Arduino. If you already have the parts, or would rather just make your own, they give you a parts list. They also have a paper layout sheet you can lay over the breadboard (or just use a reference) to see how everything hooks up onto the board. They hope to have the kt available soon.
Earthshine Design did their own breadboard-based Arduino (above). You can find info on their version here.