Usando bordes transparentes, se pueden generar infinidad de formas usando css:

.multiborde { border-color: green red blue orange; border-style:solid; border-width:20px; width:0; height:0; }

.flechaiz { border-color:transparent #000 transparent transparent; border-style:solid; border-width:10px 20px 10px 0; width:0; }

.flechader { border-color:transparent transparent transparent #000; border-style:solid; border-width:10px 10px 10px 20px; width:0; }

.flechatop { border-color:transparent transparent #000000; border-style:solid; border-width:0 13px 13px; width:0; }

.flechabot { border-color:transparent transparent #000000; border-style:solid; border-width:0 13px 13px; width:0; }