Google Gmail Multiple Account Logins

You can now use Google email with multiple accounts natively. To do so, set your bookmark directly to mail.google.com.

When you open google, you'll be prompted to login. It seems like which ever account you login with first will become your default account.

Once you've logged in, you can login to another account by clicking on your name in the top right corner. Select the other account or select Add Account to add another.