Atro-phex with 7-keto DHEA is meant to be one of the best.
However, I really don't think any of the OTC fat burners work all that well unless you are under 14-16% bodyfat.
They really are more of a 'finisher' when burning off fat.
They won't get the job done unless diet and training is also consistent and effective.
I have used a few, but only in the last stages of my comp prep, and the ones I have liked are Animal Cuts, San Tight, and I just got a bottle of ZIP from the protein factory I am going to try.
There is a problem with a lot of fat burners is that they are mostly based on caffeine, and too much caffeine just increases cortisol, which will have a rebound effect for putting fat on later, and usually around the middle.
ZIP looks promising as it doesn't have caffeine in it.