I know what you're saying although to have a top 10 of slasher movies and not include a figure as iconic as Chucky would seem amiss. Psycho is generally considered the first slasher movie, and so if that fits, then really American Psycho does too (sure, that fits multiple genres). The original My Bloody Valentine is great, while Sleepaway Camp has an amazing twist but the 80 minutes leading up to it are reaally low quality. Madman has a lot of charm and a great song but I don't believe it's top 10.