Site / blog sponsorships. I'm not talking text link ads but actual sponsorships from key companies in my sector. It's not big money but enough for me to spend my time working on what I want rather than what I have to.
In the past, I had revenue generating webapps, but I sold those in order to build some capital for future projects, savings, etc. I should probably get on to building another to be fair..
Oh, some low-maintenance Web hosting and domain registrations too for ultra old Web design clients (when I did that sort of thing). Keeps the servers paid up for me to use for my own stuff :)