Ideally, I think anything you can hold should be a weapon. Swords, axes, wood axes, spades, hoes, tomatoes, pieces of log, unfinished pieces of wall... Cataclysm has modeled this best - every item has a defined weight, blunt, slash, and pierce. "Movement points used per attack" is derived from the weight and size, and the damage dealt is based on the damage data and your strength and skill with that type of attack. So you can use a sword to swing around, or you can grab a gold bar and bash people with it. Literally every item is a weapon, simply because every item (including corpses) has values defined.
While I'm on the subject though, I had an idea for weapons... It's very abstract, not sure if I'd use it for this particular game, but it could be incredibly fun. The basic idea is to let the player create any weapon they could design. The design method would be a grid of tiles, and on each tile you can define a thickness. The thickness would range from "razor thin" to "it's a solid rock" and would determine the difficulty of creating and the weapon properties. For instance, a sword would be defined as a row of thin bits, a row of thicker bits, and another row of thin bits - or just the one edge if you're ok with that. When used as an attack, then it would act as if the leading edge struck the enemy. Thin parts would be more likely to penetrate, while higher surface area would cause a loss of force and more shallow penetration, with very large weapons just resorting to blunt damage. In this way, you could design a pickaxe made for penetrating armor, much like an ice-climber's hand pick. Or you could make a hammer with a spike in the middle of the head, so that the large weight would give you a sure penetration and then the following blunt would shatter the weakened structure. Certain properties would be used for tools as well, like the edge size would count for chopping wood or harvesting crops, while the size of the blunt face would be used for metalwork or driving nails. If a piece was too thin, it would be likely to dull or break off entirely, so razor swords would shatter too frequently, and the weight of the weapon would determine its impact force, so an axe for splitting firewood would need a lot of weight behind it. Ideally each weapon would have three modes, to swing, thrust, or swing the rear side. It should be entirely possible to make a pickaxe with a sharp point and a large blunted backside, so that you could mine your ore, then flip the weapon over and pound it into ingots.
But I don't think I'll be using this in this particular game. It seems a bit too complicated for the setting, though it would be extremely fun to see how players design their weapons and how they handle different materials. After all, an iron razor sword would surely shatter, but perhaps copper bends a little more and would hold up longer?