Google has a pretty wonderful API for rendering charts. You pass it the specifications of the chart you'd like in the URL, and it spits back a rather pretty image. It's nice not to have to play around with graphing libraries and the like. And, even if you're using Gruff, it'd take you quite a while to get something looking as good.
Only thing is that I wouldn't be too happy with just storing my data in a URL. So, if I were writing a blog post I'd want some way to store the graph data server-side, and generate the URL on the fly. Maybe a nice XML processor that reads a data file. I might get to work on that.
Playing around with world maps: