The Shapes of CSS

All of the below use only a single HTML element. Any kind of CSS goes, as long as it's supported in at least one browser.

Square

Rectangle

Circle

Oval

Triangle Up

Triangle Down

Triangle Left

Triangle Right

Triangle Top Left

Triangle Top Right

Triangle Bottom Left

Triangle Bottom Right

Curved Tail Arrowvia Ando Razafimandimby

Trapezoid

Parallelogram

Star (6-points)

Star (5-points)via Kit MacAllister

Pentagon

Hexagon

Octagon

Heartvia Nicolas Gallagher

Infinityvia Nicolas Gallagher

Diamond Squarevia Joseph Silber

Diamond Shieldvia Joseph Silber

Diamond Narrowvia Joseph Silber

Cut Diamondvia Alexander Futekov

Egg

Pac-Man

Talk Bubble

12 Point Burstvia Alan Johnson

8 Point Burstvia Alan Johnson

Yin Yangvia Alexander Futekov

Badge Ribbonvia Catalin Rosu

Space Invadervia Vlad Zinculescu

TV Screen

Chevronvia Anthony Ticknor

Magnifying Glass

Facebook Iconvia Nathan Swartz

Moonvia Omid Rasouli

Flagvia Zoe Rooney

Conevia Omid Rasouli

Crossvia Kaya Basharan

Basevia Josh Rodgers

Pointervia Amsakanna Freethinker