I would (and actually do) sponsor small projects I find useful for my business. Derick Rethans’ Xdebug, Ondrej Sury’s backport Debian repos, etc.

I’ve also made one off donations to get a higher priority fix for a bug/issue.

My list begins with Firefox, Ubuntu & linux. I want to see OS, desktops and browsers not being solely controlled by for-profit corps. In the same line, mobile OSes don't have a good alternative. Any suggestions?