In working on D&D house rules, I hit upon a method for creating balanced new D20 weapons. This might even be posted elsewhere or something, but I think that it works pretty damn well, and so if you want to come up with crazy unique weapons for your setting, use this simple system.
Base unarmed weapon 1d3
Determine a total number of points based on the kind of weapon you are creating.
light +1, medium +2, heavy +3
simple +1, martial +2, exotic +3
1 pick = upgrade damage die, upgrade critical range, upgrade critical multiplier
Then you spend the points to upgrade your weapon compared to a basic unarmed strike from an untrained person.
rapier: light martial 3, up to 1d6 (1), upgrade critical threat to 18-20 (2)
bastard sword: medium exotic 5, dice up to 1d10 (3), threat up to 19-20 (1) -hmm…one ‘pick’ left
kukri: light martial 3, dice up to 1d4 (1) threat range up to 18-20 (2)
greataxe: heavy martial 5, dice up to 1d12 (4), crit multiplier up to x3 (1)
longbow: heavy martial missile 3, dice up to 1d8 (2), crit multiplier to x3 (1)
light crossbow: heavy simple missile 2, dice up to 1d8 (2), crit range to 19-20 (1), move action to load (-1)
Anyway, you get the basic idea.