In dark skies, the Nebula in Orion (M42 in particular) is naked eye visible. As Mike says, add a pair of binoculars (from, say 7x magnification to higher) and it is a marvellous sight. In my 8" reflector, the nebulosity in the "Sword" is lovely and, with dark skies and eyes adjusted, I can start to make out the dust lanes in the Flame Nebula near Orion's belt.
More experienced observers say that you can start to pick up colour in the nebula with a 12" reflector.
I hope this helps.
