for volunteers, i cheat - we get kids from highschool work-experience programs all through the school year, and full time volunteers for 3 months at a time from katimavik, a canada-wide youth volunteer program (the bike dump could probably get on this). with so many young, energetic bodies in the workshop, community volunteers come in and are blown away by how much is going on. they like the social aspect of it (jonathan was right on), enjoy being in the shop and come back. we invite them to parties, drag them out to critical mass, encourage them to bring in music, etc.
as for stuff, after running around after donations for years we're stacked to the tits and having to turn people away. after a while, enough people know about what you're doing and want to support it that storage space and processing becomes a bigger problem than sourcing donations. but in the interim, churches and schools (bike drives), universities (end of year student clear out), large appartment buildings (they clean out their bike rooms once every couple of years), bike shops, community groups (the knights of columbus helped organize a bike drive for us last year and we got 450 bikes in one day), are all good sources for donated bikes.
hope that helps,
omar bhimji project manager pedal bike depot p. 604.708.4992