My top picks. Super cool causes, check out their websites regardless of whether you're feeling philanthropic:

  1. Represent.Us seeks to end the [as-yet legal] political corruption in the US that negatively impacts us all, regardless of party preference. This is my TOP PICK, because I believe all other crucial change [like avoiding environmental disaster] will not be possible without addressing political and corporatist roles in promoting [or preventing] a sustainable future.

  2. The Ocean Cleanup: getting that dang plastic out of our ocean, yo! Posthaste!

  3. Vasalgel via the Parsemus Foundation: a reversible, long-term contraceptive for men. I could soapbox for days on what I think the profound social implications of this would be!

  4. Sunlight Foundation: dedicated to creating transparency and accountability in our government by unearthing the specifics on who's paying out our politicians.

Related to my cycling trips:

  1. EuroVelo is working on bike trails for the route that I plan to complete in 2021! The more of it gets done, the better that’ll be for me and many others.

  2. East Coast Greenway is building a continuous non-motorist route along the entire Atlantic coast [precisely my route up the Eastern Seaboard in 2015]. I got hit by a speeding car in South Carolina because there were no safe paths for me to take. The completion of this trail would minimize risk to future cyclists!

Local organizations I've visited and/or donated to on my US trip [psst, if you'd like to suggest a local charity along my future routes, drop me a line]:

Key West Wildlife Rescue in Key West, FL, is refreshingly transparent [you can visit for free, but the center is decidedly not oriented towards tourists, but on their actual stated mission...]; rehabilitates and releases local birds and other animals.
The Turtle Hospital in Marathon, FL is quite sophisticated; rehabilitates and releases threatened sea turtles [like them on Facebook for updates!]

Some others that I like [in California and Nevada, two of my main stomping grounds] are Reno Bike ProjectChrysalis Community Counseling ServicesCommon VisionUrban TilthRichmond Trees.

For larger charities, check out the listings on Charity NavigatorCharityWatch, and the BBB Wise Giving Alliance, who all vet charities for effectiveness, transparency, etc. and categorize them so that you can find a cause in support of something that speaks to your own values and hopes.