Paid builds. You get Access to the source code but you can either build yourself or pay a small amount to have a packaged built and updated whenever.
I also like the twice a year nag screen thunderbird or Wikipedia uses (KDE was right to start doing it too, in my books).
I don’t believe a small donate button in the “about” section of the settings screen is of any use.
Liberapay is a good way to regularly give to open projects with out having to remember to go back to a project page. A european equivalent to patreon for FOSS projects and creators.