If you are addicted to offline gambling, there is not much I can help, but as an online gambler, this is something that I have made myself to do:

Create a simple HTML webpage with links to various forums, Tumblr, Top 10 Lists, etc, which takes some time(10-15 mins) to read,
Use a bookmark to get access to this page fast,

Try to reduce the time that you spend on the gambling sites by half an hour per week, and during  these times go to the sites in your custom webpage.
Also, if you ever feel like you are going to lose much while doing it, immediately click the bookmark, and start reading. It will help a lot.