Sodium Pentothal. Removed inhibitions and makes you more willing to talk. I don't think it's necessarily truth serum, but you're so relaxed you'll probably give something away.
Hell, a few beers work does the same thing for me. I myself wouldn't mind being wrapped up in Wonder Woman's golden lasso
(Whoops...too much truth there)
Creepy, crazy, worthless, candidate to scrub warp conduits...take your pick.