Hot answers tagged charities
The best option would be to find a local bicycle co-op and offer them the parts. (They would probably welcome bikes, rims, and tools.) You may not be near a co-op; if that's the case, there are numerous "pay it forward" threads on bicycle forums, but you'd end up paying postage; useful for small or esoteric parts. (I've given away a lot of stuff that way.) ...
There is a Wiki with an International List of Bike Collectives and Community Orgainizations at BikeCollectives.org. There are many other organizations, like the Salvation Army in the US, that take almost any item and either operate second-hand stores or sell the items to other thrift shops. I prefer to deal with organizations like the Salt Lake City Bike ...
I am not sure how you would find the individual rides with the highest participation, but there are a few organizations that reach thousands of cyclists across the US by holding rides in several communities. In the US you tend to rarely see huge rides because the logistics and regulation hoops in many areas is to great to overcome. Many rides are capped ...
In Madison, Wisconsin, Red Bikes will take old bikes. Budget Bicycle Center on Regent Street is the dropoff location.
In Boulder, Colorado, Community Cycles accepts donated bicycles and puts them to good use. Their website lists other bike collectives across North America that may make a good starting point for finding a similar organization elsewhere.
If you've tried all of the charities and bike co-ops in your area and are still left with a pile of parts, you could try offering them (free or for a nominal charge) to the bike hackers over on the Atomic Zombie Forums (or somewhere similar). If they're parts then they'll probably be glad of them, if they're frames then they'll probably only take them if ...
The London to Brighton Bike Ride organized by the British Heart Foundation is the largest UK one, probably the largest in Europe. That has 27,000 participants.
The 2013 Ride For Roswell Park Cancer research hospital drew a reported 9000 riders. The hospital is located in Buffalo New York. Additionally it features a 200 rider peloton the evening before prior to opening ceremonies. The ride winds through the city from the hospital to the University of Buffalo Amherst campus covering 13.5 miles.
I would just look for ads and/or post an ad on craigslist/kijiji. I just saw an ad last week for someone looking for "old bike parts in any condition". I kept the parts that I knew I could fix and that I would need and dropped the rest off to him.
Only top voted, non community-wiki answers of a minimum length are eligible