Google has added Multiple-Factor authentication for users of Gmail and Google Apps, other Google services too.
Using your Cell phone, Google will call your cell and read you a 6 digit code that you enter after you have already entered your username and password. This solution adds 'something you have' (your cell) to the ’something you know' (username and password) to improve your Google account from being attacked by brute force password guessing and any weak passwords you might be using.
Someone with your username and password would be unable to login to your Google account without your cell phone once activated.
Similar to Verisign/Symantec VIP solution for eBay & PayPal there is an App for your smart device as well. Check out Google Authenticator for your iDevice, BlackBerry and Droid.
Google Authenticator How to enable Help
SC Magazine article on Ggogle's new authentication method