Birdy

Cowboy Bebop

Dragonball

Flame of Recca

Gundam Wing

Hunter x Hunter

Inuyasha

Mononoke Hime

Oddments

Outlaw Star

Ranma 1/2

Rurouni Kenshin

Trigun

Yuu Yuu Hakusho

Sunny Saiyan
Goku is just an upbeat kind of guy, even when the villains are closing in. Here's a nice cel with a typically sunny expression.
 
Added: 5/19/02
 
Sunny Saiyan