We hear about websites getting compromised all the time, but it's hard to keep track of all of them. If you're worried a site you've registered for might be hacked, Hacknotifier cross checks your email against a massive database of hacked passwords.
Hacknotifier searches for your email address in publicly available hacked databases. All you need to do to check is type in your password on the main page and it will cross-reference it and give you its results in seconds, no registration or payment is required. If you want 24-hour security, the site offers two plans of $US5 and $US7 per year for constant monitoring and notification.