Classical - This is the traditional shape guitar pick.

Triplet - An equilateral triangle shape. This pick has 3 identical corners meaning it can be used equaly on all sides.

Jazz - A small size pick, usually prefered by Jazz players.

Teardrop - Another small size pick. This is the regular teardrop shape.

Thickness: 

The thickness of the picks ranges from 1mm up to 5mm and sometimes more. The thicker picks are beveled down to 1mm in order to achieve the same accuracy as in the thin picks. It is possible to put "grip grooves" on thick picks without risking the strength of the pick. The Grip Grooves help to grip the smooth pick especially when hands are sweaty.