Cleric 1d8 (1d6 ranged, unarmed or improvised)
Fighter 1d10 (1d8 ranged, unarmed or improvised)
Thief 1d8 (1d6 ranged, unarmed or improvised)
Wizard 1d6 (1d4 ranged, unarmed or improvised)
I'm being cheeky but I think class-based damage works really well and it's very simple and flexible...