Pedal Parts Plus is a great little website for all your guitar and bass effect pedals parts. They have a wide variety of switches, resistors, diodes, capacitors, and everything else you need to build your first or your umpteenth effect pedal.
The prices on this site are great. Some of the cheapest (yet still quality) 3PDT switches I've seen (as low as $3.80 ea.). My order got to me quick was well packaged so there wasn't any risk of bumps or bruises from the postal service. Highly recommended.