Melatonin, Valerian Root, and Kava Kava are all OTC herbs that can help. Additionally 5-HTP (which we all know helps X users after a roll) also is a great sleep aid.
Benadryl works pretty well also and is of course used as a antihistemine (sp?).
Valium, Xanax, Sonata, Ambien, ect are all prescribed sleep aids that work great!! Probably the best being Sonata due to it short half-life it has great clearance times. You can take a Sonata at midnight wake up at 6am and have no after effects. Of course you can always go south if you don't have a prescription.