You can go for diazepam or alprazolam, but they aren't real hypnotics (especially alprazolam) and, although I believe they will work initially, I don't think they have staying power like a true hypnotic. Diazepam may be a better choice than alprazolam, however.
There's also temazepam, triazolam or nitrazepam (if you are outside the US for this one) are true hypnotics and will probably work better for you for a knock out blow.
If you don't want to go the benzo route there is trazodone and it works very well. You may also want to keep quetiapine (Seroquel) in mind also.