Goblins are detailed on p.107 of the Monster Manual (3.0).
Goblins are small humanoids. Their skin and eye color runs from red, through orange, to dark yellow (although almost never the same eye and skin color). They have broad faces with wide noses and sloping forheads. Pointed ears and wide mouths (full of sharp teeth) also make them unappealing to humans. Their arms are long in proportion to their bodies (when compared to humans).