How to move Lion installer to another Mac?
Unfortunately the installer package contains the source files for the installation and this package is deleted once installation has completed.

If you still have the installer in Applications, right-click on it and Show Package Contents then browse to the /Contents/SharedSupport/ folder and look for the InstallESD.dmg disk image. This image can be burnt to a dvd saving future downloads but I am afraid you are going to have to download it again.