Here you'll find a range off shapes all coded with just pure CSS3 code. Unfortunately not all shapes will render correctly in all browsers, currently only web browsers that support CSS3 will produce the correct geometric shapes.

Square

#square {
   width: 140px; 
   height: 140px; 
   background: blue; 
}

Circle

#circle { 
   width: 140px;
   height: 140px;
   background: blue; 
   -moz-border-radius: 70px; 
   -webkit-border-radius: 70px; 
   border-radius: 70px;
}

Oval

#oval {
   width: 200px; 
   height: 100px; 
   background: blue; 
   -moz-border-radius: 100px / 50px; 
   -webkit-border-radius: 100px / 50px; 
   border-radius: 100px / 50px;
}

Up Triangle

#up-triangle {
   width: 0; 
   height: 0; 
   border-bottom: 120px solid blue; 
   border-left: 60px solid transparent; 
   border-right: 60px solid transparent; 
}

Down Triangle

#down-triangle { 
   width: 0; 
   height: 0;
   border-top: 120px solid blue;
   border-left: 60px solid transparent; 
   border-right: 60px solid transparent; 
}

Left Triangle

#left-triangle {
   width: 0;
   height: 0;
   border-right: 100px solid blue;
   border-top: 50px solid transparent;
   border-bottom: 50px solid transparent;
}

Right Triangle

#right-triangle {
   width: 0;
   height: 0;
   border-left: 100px solid blue;
   border-top: 50px solid transparent;
   border-bottom: 50px solid transparent;
}

Triangle Top Left

#triangle-topleft { 
   width: 0; 
   height: 0; 
   border-top: 100px solid blue; 
   border-right: 100px solid transparent; 
}

Triangle Top Right

#triangle-topright { 
   width: 0; 
   height: 0; 
   border-top: 100px solid blue; 
   border-left: 100px solid transparent; 
}

Triangle Bottom Left

#triangle-bottomleft { 
   width: 0; 
   height: 0; 
   border-bottom: 100px solid blue; 
   border-right: 100px solid transparent; 
}

Triangle Bottom Right

#triangle-bottomright { 
   width: 0; 
   height: 0; 
   border-bottom: 100px solid blue; 
   border-left: 100px solid transparent; 
}

Trapezium

#trapezium {
   height: 0; 
   width: 80px;
   border-bottom: 80px solid blue;
   border-left: 40px solid transparent;
   border-right: 40px solid transparent;
}

Diamond

#diamond {
   width: 80px; 
   height: 80px; 
   background: blue;
   margin: 3px 0 0 30px;
   /* Rotate */
   -webkit-transform: rotate(-45deg);
   -moz-transform: rotate(-45deg);
   -ms-transform: rotate(-45deg);
   -o-transform: rotate(-45deg);
   transform: rotate(-45deg);
   /* Rotate Origin */
   -webkit-transform-origin: 0 100%;
   -moz-transform-origin: 0 100%;
   -ms-transform-origin: 0 100%;
   -o-transform-origin: 0 100%;
   transform-origin: 0 100%;
}

Rectangle

#rectangle {
   width: 140px; 
   height: 80px;
   background: blue;
}

Parallelogram

#parallelogram {
   width: 130px; 
   height: 75px;
   background: blue;
   /* Skew */
   -webkit-transform: skew(20deg); 
   -moz-transform: skew(20deg); 
   -o-transform: skew(20deg);
   transform: skew(20deg);
}

Twelve Point Star

#twelve-point-star {
   height: 100px;
   width: 100px;
   background: blue;
   position: absolute;
}
#twelve-point-star:before {
   height: 100px;
   width: 100px;
   background: blue;
   content:"";
   position: absolute;
   /* Rotate */
   -moz-transform: rotate(30deg);
   -webkit-transform: rotate(30deg);
   -ms-transform: rotate(30deg);
   -o-transform: rotate(30deg);
   transform: rotate(30deg);
}
#twelve-point-star:after {
   height: 100px;
   width: 100px;
   background: blue;
   content:"";
   position: absolute;
   /* Rotate */
   -moz-transform: rotate(-30deg);
   -webkit-transform: rotate(-30deg);
   -ms-transform: rotate(-30deg);
   -o-transform: rotate(-30deg);
   transform: rotate(-30deg);
}

Six Point Star

#six-point-star {
   position: absolute;
   width: 0; 
   height: 0; 
   border-left: 50px solid transparent; 
   border-right: 50px solid transparent; 
   border-bottom: 80px solid blue;
}
#six-point-star:after {
   content:"";
   position: absolute;
   width: 0; 
   height: 0; 
   border-left: 50px solid transparent; 
   border-right: 50px solid transparent; 
   border-top: 80px solid blue;
   margin: 30px 0 0 -50px;
}

Speech Bubble

#speech-bubble {
   width: 120px; 
   height: 80px; 
   background: blue;
   position: absolute;
   -moz-border-radius: 10px; 
   -webkit-border-radius: 10px; 
   border-radius: 10px;
}
#speech-bubble:before {
   content:"";
   position: absolute;
   width: 0;
   height: 0;
   border-top: 13px solid transparent;
   border-right: 26px solid blue;
   border-bottom: 13px solid transparent;
   margin: 13px 0 0 -25px;
}

Egg

#egg {
   display:block;
   width:126px; 
/* width has to be 70% of height */
/* could use width:70%; in a square container */
   height:180px;
   background-color:blue;

/* beware that Safari needs actual
 px for border radius (bug) */
   -webkit-border-radius:63px 63px 63px 63px/
   108px 108px 72px 72px;
   /* fails in Safari, but overwrites in Chrome */
   border-radius:50% 50% 50% 50%/60% 60% 40% 40%;
}

EQ Triangle

#eq-triangle {
  width: 0;
  height: 0;
  border-bottom: 104px solid blue;
  /* 104 = 120 * 0.866 */
  border-left: 60px solid transparent;
  border-right: 60px solid transparent;
}

Pacman

#pacman {
  width: 0px;
  height: 0px;
  border-right: 60px solid transparent;
  border-top: 60px solid blue;
  border-left: 60px solid blue;
  border-bottom: 60px solid blue;
  border-top-left-radius: 60px;
  border-top-right-radius: 60px;
  border-bottom-left-radius: 60px;
  border-bottom-right-radius: 60px;
}

Biohazard

#biohazard {
  width: 0;
  height: 0;
  border-bottom: 60px solid black;
  border-top: 60px solid black;
  border-left: 60px solid yellow;
  border-right: 60px solid yellow;
  -moz-border-radius: 60px; 
  -webkit-border-radius: 60px; 
  border-radius: 60px;
}

Heart

#heart { 
	position: relative;
}
#heart:before, #heart:after {
   position: absolute;
   content: "";
   left: 70px; top: 0;
   width: 70px;
   height: 115px;
   background: blue;
   -moz-border-radius: 50px 50px 0 0;
   border-radius: 50px 50px 0 0;
   -webkit-transform: rotate(-45deg);
   -moz-transform: rotate(-45deg);
   -ms-transform: rotate(-45deg);
   -o-transform: rotate(-45deg);
   transform: rotate(-45deg);
   -webkit-transform-origin: 0 100%;
   -moz-transform-origin: 0 100%;
   -ms-transform-origin: 0 100%;
   -o-transform-origin: 0 100%;
   transform-origin: 0 100%;
}
#heart:after { 
left: 0; 
   -webkit-transform: rotate(45deg); 
   -moz-transform: rotate(45deg); 
   -ms-transform: rotate(45deg); 
   -o-transform: rotate(45deg);
   transform: rotate(45deg);
   -webkit-transform-origin: 100% 100%;
   -moz-transform-origin: 100% 100%;
   -ms-transform-origin: 100% 100%;
   -o-transform-origin: 100% 100%;
   transform-origin :100% 100%;
}

Yin Yang

#yin-yang {
   width: 96px;
   height: 48px;
   background: #eee;
   border-color: red;
   border-style: solid;
   border-width: 2px 2px 50px 2px;
   border-radius: 100%;
   position: relative;
}
#yin-yang:before {
   content: "";
   position: absolute;
   top: 50%;
   left: 0;
   background: #eee;
   border: 18px solid red;
   border-radius: 100%;
   width: 12px;
   height: 12px;
}
#yin-yang:after {
   content: "";
   position: absolute;
   top: 50%;
   left: 50%;
   background: red;
   border: 18px solid #eee;
   border-radius:100%;
   width: 12px;
   height: 12px;
} 

Octagon

#octagon {
   width: 100px; 
   height: 100px; 
   background: blue;
   position:relative;
}
#octagon:before {
   height: 0;
   width: 40px;
   content:"";
   position: absolute; 
   border-bottom: 30px solid blue;
   border-left: 30px solid white; 
   border-right: 30px solid white; 
}
#octagon:after {
   height: 0;
   width: 40px;
   content:"";
   position: absolute; 
   border-top: 30px solid blue; 
   border-left: 30px solid white;  
   border-right: 30px solid white; 
   margin: 70px 0 0 0;
}