Try Sound Manager. Schedule volumes of types of sounds with it (6 categories). Switch off notification (Battery full, e-mail notification etc.) volume from 12 to 7 while leaving untouched ring and media volumes and you're all set. Works on my brandnew Samsung Galaxy s2.
Slept well last night without a disturbance! I used to swich to buzz only before going to sleep and to remember to switch it back to ring in the morning.
Sleep well!
TheyGowByrd