Last Updated Jan 17, 2011 10:24 PM EST
It's actually pretty simple, First, make sure you've enabled Gmail's support for opening multiple accounts at once. Visit http://google.com/accounts and turn on Multiple Sign-ins.
Next, open a Gmail account. You'll see that your account name at the top of the browser now has a drop-down. You can switch to other accounts or long in to another account rom here.
Here's the interesting part: The URL of each of your e-mail accounts is very similar, differentiated only by a number (1 is your primary account, 2 is your next account, and so on). Just bookmark each of these pages, or drag them to your Favorites bar, to get immediate access to them. It's simple, and it works!
Photo courtesy Flickr user gliuoo