Does anyone have tips on high converting (or click rate) "Add to Cart" and "Checkout" buttons?

My current template uses all black buttons with small white text. All buttons on the product page look essentially the same. Does anyone have any tips, or actual buttons, that can improve the conversion rates? My feeling is that the "Add to Cart" button gets lost on the page somewhat. I could just make it green or blue, while leaving the others as they are, but I am looking for advice from someone that has maybe conducted some analytics or funnel testing on different buttons.

I would very much appreciate ideas on this. I apologize if there was a better category for this thread.