Are there any natural or OTC male enhancement supplements?

There are, and they've been given numerous clinical trials. The one that has the most promise is Yohimbe extract, but thus far - and that's after over ten years of intensive testing - it is little more effective than placebo. The rest - well, you'll find all kinds of testimonials and advertisements saying they're the greatest thing since Adam met Eve - but that's pure, unadulterated b.u.l.l.s.h.i.t ! They are all totally ineffective. Period.