Android FAQ: How do I get a list of Android devices on my computer system (Android AVD devices and physical devices that are currently attached)?
At your command line, just use the adb devices command from the Android SDK:
This will list all the names of AVD devices and physical devices currently installed on your computer.
You can also get this listing from within Eclipse. I don't have Eclipse open at the moment, but the Android menu options are either under the Window or Help menus.
Note: If you don't have your PATH set up, you'll find the adb command in the platform-tools subdirectory of your Android SDK installation directory.