avr-objdump -S myprogram.cpp.elf > listfile.txt
(The programm avr-objdump.exe can be found in the directory Arduino\hardware\tools\avr\bin\.)
With some versions of the Arduino IDE the temporary *.elf file will be deleted after you have saved the source program.
You also can read back the compiled file from the flash memory of the microcontroller (provided the fuses have not been set to disable this option). The command
avrdude -F -V -c arduino -p ATMEGA328P -P COM5 -b 9600 -U flash:r:flash_backup.hex:i
gives you a backup of what is in the flash memory. Of course, you have to provide the correct parameters instead of "-P com5" (port number) and "-b 9600" (baud rate).
The file flash_backup.hex can be made readable with the program ReAvr .
But it's no fun to read what it produces.