And below, one of my favorites... This lavender lace racerback bra! (wendyslookbook.com)
I had to wear a low racerback bra as the straps cut in towards the shoulders so regular bra straps would show and there is a keyhole back. (renttherunway.com)
This can show the sides of a strapless or racerback bra because of it's side cut. (adashofpretty.com)