Just get into your router config and block sites that you know will suck you in (ex: reddit or digg), on your workstation. I personally block them during "my work hours", that way I have something to look forward to after I've got my work done.
It also helps to have a router config that makes it difficult and time intensive enough to make a change, that wat it's easier to just NOT make the change and get back to work.
It also helps to have a router config that makes it difficult and time intensive enough to make a change, that wat it's easier to just NOT make the change and get back to work.