Amethyst is one of the best dream crystals. It opens multidimensional awareness, and links our emotional bodies with the spiritual. Whenever I sleep with an Amethyst tucked in my pillowcase I have vivid dreams that I remember easily.
It is also a relaxant, and a natural tranquilizer~ helps you reach meditative states. So it is an excellent stone to both help you get to sleep and to aid in reaching profound dream states.