I've done Python and PHP and am almost done completing Ruby, I went from PHP -> Python -> Ruby myself. I like Python out of all three, personally.
@steven.copeland you seem to have done mostly Web based languages, doing PHP would complete the web side of things.
Or Python is fun if you want to move into game making rather than just sticking totally on the web. But taking Python will be a good first step to understanding Django which is what a lot of websites use as a framework these days. So i would say Python would be the most interesting
Yeah I think Python seems like a pretty good idea.