Ask HN: How do you avoid distractions like HN?

I am a student and work part time on my own projects. Because I am self-employed and have no real schedule, I sometimes find it hard to concentrate on my work. I sit down with the intention of programming, but very soon end up with tabs open on Hacker News, StackOverflow, and Planet Django. Even when I am concentrated on my programming, I sometimes regress and start reading interesting articles if they are related to my current project or programming language. In part, this is due to the fact that I spend a lot of time on Google looking up programming questions.

In order to overcome my distraction, I use "mediums" to trick myself into focusing. I have found that having a cup of coffee on the desk will put me in the right mindset, because I always use coffee when working. This works well, but I don't enjoy being dependent on hacks like this.

Do you have any tips for becoming and remaining productive?