MSN Toolbar is the latest of the toolbars, but is starting to gain popularity. As with Yahoo! and Google toolbars, it allows other features on top of pop-up blocking. Below is the MSN Toolbar:
The following icon is the Pop-up Blocker: 
To disable pop-up blocking, click on the Down Arrow to the right of the text to bring up the Menu:
Click on Allow Pop-ups. To turn the Pop-up Blocker back on, you go back in and recheck the entry to re-enable their Pop-up Blocker.