I take this:
http://www.pronutrition.ro/produs.aspx?pID=173&cID=0&dID=0&bID=38I haven't exactly made a buy of it but it was a promotion of proteins + this so I got it. To be honest, it does help. Not sure if it's placebo or not, probably not though, but when you squat you do have some extra energy and "nerve" (extra will so to speak) to complete your reps and not quit. So...
It's a Romanian product though, so unless you can translate that ... here's what it contains (in Romanian):

You can also go with this: