MacCentral led me to Macworld: Feature: Software Bargains: Productivity tools: New and updated reviews of awesome free and low-cost software by Dan Frakes which led me to Sidenote 1.7 On-Screen Note App.
Sidenote hides a notepad that supports rich text, images, and PDFs on the edge of your screen — the notepad appears when you move the cursor to the screen edge, and it slides off the screen when not in use. You can create multiple notes and use the keyboard or a pop-up menu to switch between them. You can even drag content from the Finder or another application to Sidenote; the Sidenote notepad slides out to accept the content (free).
I use StickyBrain for keeping notes and snippets, but am always open to having another quick-use application at hand. Sidenote looks good and seems to work well. It’s essentially invisible, until you need it, and it’s hard to beat the price.