One of the best features of Apple's Entourage and Microsoft's Outlook is the ability to work in several different windows, making composing emails, reading responses, and searching your inbox easy to do without navigating between screens. I figured out a way to do this a while ago, but now Gmail contains this functionality right on the page.
Clicking on the "new window" icon on the top right corner of your Gmail screen will take the window you're working in and open it in its own window. Then, use the original window to search your inbox, pull up an old email, or check your sent items. (You can still use the shift+click option to do the same, if you prefer.) If you open windows to save for later, be careful; the new windows will not stay open once you close your main Gmail screen. Also, this feature doesn't work in Internet Explorer — you'll have to use Chrome, Firefox, or Safari.