Everyone uses their software, firewalls, servers, email serves, openssl is everywhere, corporate/bank cluster without BSD or Linux with grsecurity is unimaginable.
I recently started donating to opensource project I use everyday. I realised how little they ask for, F-Droid, I easily doubled their BTC found used to cover server maintenance, LibreOffice asks for 3EURO donation by default (also BTC)! OpenBSDFundation asks for 10$ per month.
https://grsecurity.net/contribute.php
Edit: I also found a nice way how to donate to Tor, there is a site https://oniontip.com/ where you can donate others for running Tor nodes, one of two top 200nodes has WikiLeaks BTC address, another one goes to my wallet and I send it back to TorProject. I had enough free resources, I used them :)