KeepMeOut is a site with an interesting concept. Basically the site allows you to block yoursef from sites you specify for short periods of time.
- Gate keeper for short periods of time
- Time tracker
- You have to create a bookmark for every site you want to "block"
- If you use multiple browsers you have to manually sync your bookmarks - unless you use something like foxmarks
- You can get around this by typing the address on the browser
Still if there is that little site you are struggling with (meaning you visit ALL the time) this might be worth giving it a shot.