Impero. Program that lets us get up a thumbnail view of very student logged on. We can't watch all the time, but they never know when we might be watching. We also have a review system where any teacher can email us about legitimate sites they want to be given exceptions. This means that if they do find a new unblocked site that our filter provider has yet to classify, we swiftly notice it. And kill it.
Pornography is actually a very rare problem for us. It comes up sometimes, but few students seek it out while in school - probably because they don't have the privacy. They do love flash games though, and general time-wasting meme sites and image board, and movie streaming sites of dubious legality.