Some that spring to mind (spelling is most likely wrong for these):
Mugwort (Artemisia vulgeris) - Basically a dream-herb. Supposedly enhances dream-recall/vividness.
Valerian (Valerian officinalis) - A anti-anxiety, cramp plant. Also aids in sleep.
Melatonin (Melatonin is the scientific term?) - Mostly used to reduces things like jet-lag i think, it a chemical naturally produced by some gland in the human body. It regulates sleep, et cetera.

I haven't tried any of these so, yeah. I may also have remembered incorrectly what they actually do, lol.

Maybe try erowid.com probably find something there.

Ohwell, good luck and have fun!