I'd go with Xanax... when I'm coming down from acid, my mind is too stimulated to goto sleep. Xanax takes off that anxious edge and gives you the necessary drowsiness... just find someone that suffers from panic attacks and they're probably prescribed it... or some other type of benzo(i'm pretty sure any one will do)... offer them $5 for 2mgs... most people will say that that's too much to pay, but it's totally worth it when you're begging for some Z's at eight in the morning.
I don't suggest smoking weed, because in my experience, weed potentiates acid and also has a tendency to bring the trip back... this does not promote sleep
alcohol is good for most, but for me it doesn't make me tired, but regardless... it's fun to binge drink in the wee hours of the morning
I use to take melatonin pills for this a while back. They're a natural sleep aid that is available for cheap at GNC.
GHB sounds like a great idea, but i've yet to try it
Last time i was in your situation, I took 20mgs of hydrocodone and it worked like a charm.
hope i was some help... goodluck