Google Charts API
Posted on January 6, 2010
While working on one of my most recent iPhone apps I had the need for a graph. I did a quick search for an open source plotting library and stubmled upon the google charts api. You make a simple request with a URL and it returns a png image with data you provide in the URL. This worked perfectly for my needs.
Obviously this wouldn't be a good solution if your app didn't inherently need an internet connection, but the app I was working already needed one to download data.