Well, you could just load any character up with magic items. W of X-Ray vision, X of flying, Y of speed, Z of Invulnerability.
If you wanted to replicate Superman's powers with inherent class abilities, I think you'd have to go Monk/Sorcerer. You'd need Stoneskin, the resist elements spells, haste, fly, jump, cone of cold, flame arrow ("flame eye ray", that is) and... something for x-ray vision. The monk levels would be for Unarmed attacks bonus and AC, as well as other immunities.
Actually, no, Superman was Superman because he was from Krypton. So, just make a new race:
Attribute bonuses: +18 to all stats.
Features: X-ray vision, Fly at will, DR 20/-, Immune to poison and disease, Breath weapon: frost breath as white dragon, Produce Flame as gaze attack, permanent protection from elements, does not need to breathe/immune to exposure damage, immune to subdual damage, vulnerable to kryptonite (nullifies all other racial features).
-z
PS: I can't believe I actually replied to this.