With the most recent update to 1Password they have now added a feature called Watchtower. Watchtower checks whether a website is (or ever was) vulnerable to the heartbleed bug, then tells you whether its safe to update your password.
Once you have loaded the application you will need to enable this is run in the preferences. This will then show you a list of all the logins that they recommend you change your password for.
Currently this is only on 1Password for the Mac, the windows version currently does not have this version.
They also have added a site which you can use to check a website.
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