Many music lovers can't live without music. So even they are going to sleep, they need sleep to their tunes. It's a good habit because you may have a higher quality of sleep. Here 3 iTunes sleep timer are introduced. They will put both you and your Mac to sleep after the end of music.
iTunes Timer - Mac Dashboard Widget
This Mac OS X dashboard widget let you enjoy listening to music, audio books, podcasts, radio in iTunes until the countdown is complete. After installed, just use the slider bar to set the countdown and click the green button to start the timer.
With additional options, you could also control QuickTime, DVD Player and put your Mac into sleep mode.
iTunes Sleep Timer - Yahoo Widget
This is a Yahoo Widget based iTunes sleep timer for free. After the designated time duration complete, it pauses the iTunes so that you can dream for the rest of the night. To let iTunes wake you up at specified time, you need another Yahoo widget called iTunes Alarm Clock. See more iTunes widgets from Yahoo.
iSleep - Sleep Timer and Alarm Clock
This is the paid ($9) iTunes sleep timer with more features, e.g., using a DVD instead of playing music, waiting for the movie to end before going to bed, etc. If your Mac is noisy, also put your Mac to sleep for a quiet background and saving energy.