Disable distracting websites
The first and possibly easiest thing you can do to stay focused is disable the sites that you know distract you, especially if there are certain sites you need to access in order to work. Apartment Therapy, Pinterest, Facebook, Twitter--disable them all! There are so many programs you can use for this, and most if them will allow you to set a timer for how long you want to go offline. Try SelfControl if you use a Mac, Leechblock if you're looking for a Firefox extension, or StayFocused if you use Chrome.
Use a dedicated tool for browsing
This option is really only available if you have a secondary computing device, but it's working trying if you do. Whether it's an iPad or a netbook, try doing all your work on your primary computer, and all your browsing on your secondary device. The mental jump to another device will make it a lot harder to procrastinate, as will blocking yourself entirely from browsing on your work computer.
Put your computer in "airplane mode"
In addition to the above tip, you can put your primary work computer in "airplane mode" by turning off your WiFi connection. This is especially helpful if you don't need the internet to work. Even if you do need to use the internet for work, you're bound to have some tasks that don't require staying connected. Try going without WiFi (or unplug the ethernet cable, if you're wired) just long enough to get things done.
Close programs that aren't for work
Sometimes all it takes is closing distractions. Keep your web browser, e-mail client, and chat program closed. Clean your desktop, and delete any files you don't need. While your at it, set a clean and simple wallpaper ask your desktop background. If you use a Mac, turn dock hiding on. The lack of visual clutter will inspire you to keep windows closed and stay productive.
Set a timer
Set a timer on your phone or computer, and set your mind to staying focused and not browsing the internet for that time period. 20 minutes is always a good place to start. Try something like the Pomodoro Technique and see how many times you can stay distraction free in your day!
How do you steer clear of distracting websites while you're working online? Let us know!