Robby Kraft (mostly Robby) and I threw this 555 circuit together on Wednesday night (2/25/2011) out of parts we had. Robby has an extensive and well-sorted box of capacitors and loves playing with 555s, two things which made making this circuit easy.
Robby immediately found a great 555 Timer Calculator after a minute or two of searching on Google, and we plugged in values into the calculator, and tried out different combos of capacitors, resistors, and potentiometers until we had something we liked. Total project time- about 1.5 hours, not counting collecting the parts because they were things we had already.
the parts you'll need can be easily found at Radio Shack, online at Digikey, or my favorite local supplier, URS Electronics in Portland.
Changes to Make Use a much smaller, screwdriver turned Potentiometer (already linked to in "Supplies" above.