A while ago, I started working on a sparkline font at the Khan Academy. Instead of writing some obtuse canvas script that would be hard to maintain, why not use a font to represent the same thing? The text then, could be meaningful, and you'd have the advantage that the sparkline display would gracefully degrade.
We tried it out and the project went another way, but the font remained. Please edit, hack, update, do whatever.
In this project, i'm providing it both as a css base64 encoded font (for webpages), as a UFO file and also as an OTF. I don't have any current intent to support this at the moment, but sparklines are always interesting and having tools available for implementing them is always nice.