This article provides the steps required to display the sound control on Mac OS X Lion menu bar. By default the sound control will be displayed in Menu bar and if it is not shown then you can do the following
Click the Apple icon and select Preferences from the menu list.
In the System Preferences window, navigate to Hardware section and click the Sound option.
In the Sound Preferences, mark the check box with label as Show volume in menu bar
This would display sound control in the menu bar as shown below.