Originally posted by Draklar
20 pounds, eheh... I\'d be all worked up by now with something like that ^^
Mine is 4 pounds, and still it\'s a bastard 
Thats known as a \'Hand and a Half Sword\' in more polite company

There are probably weapons that do weigh over 20lbs, but they would be rare and more specialised than lighter sword and spears, and not as suited to prolonged miltary use in a long drawn-out campaign, just by virtue of the weight of the thing tiring the user. Mauls ( essentially iron or steel-banded sledgehammers employed as a hand-to-hand weapon ) would probably have weighed that much. Its the perfect thing for killing a dismounted knight in a jiffy in a way thats likely to destroy the morale and resolve of any remaining foes. The head of this one (
http://doityourself.com/store/6480065.htm, not a medieval one but a modern equivalent ) weighs 16lbs alone, with a handle long and sturdy enough to swing it effectively that would put it over 20 lbs probably.
The heavier lances ( not carried by hand but attached to a swivel-type mountpoint on the saddle ) and halberds are probably not heavy enough to be in the same category, these halberds
http://www.slam.org/exhibits/armsandarmor/staff.html seem to max out at a bit over 6 lbs.
Any chemistry people know what volume of metal would comprise 20 lbs ( ~ 9 kg ) of steel and/or iron? It would be quite a hefty chunk I imagine.. shape it into a sword and whoever you hit with it is likely to be dead afterward. It doesnt quite match the lethality of 9kgs of plutonium though.