Unlike the older times having one email address is no longer an option that many users would prefer. Plus having multiple accounts on same service provider needs an effort to launch more than 2 different browsers to access the accounts simultaneously. Google now provides the feature of logging into your multiple accounts through the same browser.
To enable this feature go to google.com/accounts and click Edit besides the option Multiple sign-in.
In the page you are redirected to click on the check boxes that explain the rules and save. Now once you sign into your first account you can sign into the others by clicking the arrow besides your id at the top right corner. You can either toggle between different accounts or log in to a new google account.
This feature is only for the advanced users. The services in which you can use this feature are Calendar, Reader, Code , Sites and Gmail. For services like Picasa web albums and Blogger that don’t support this feature, you’ll be defaulted to the first the account you signed in with during the same session.