{tech}.Ben Buckman.net

I needed to sign a PDF on my mac, and didn't want to waste the paper and ink to print, scan, and shred it if I didn't have to. So I found this open-source app FormulatePro, which lets you add text and images to PDFs.
It's a little clunky: Images aren't in the toolbar, they're added with File -> Place Image. And it doesn't save to PDF, it just uses OSX's built-in "Print to PDF" to export. But for basic form filling/signing, it does the job for free.