THE GROSSMESSER! It's the European katana:
Made for slashing, creating deep, serious cuts and dismembering.
Here's the cold steel guys using one:
Fantastic.
EDIT: Oh yeah, and if you want to find out more about portraying medieval weapons realistically this site: http://www.thearma.org/ is excellent, and there are several Youtube enthusiasts who do a good job dispelling myths (Like this guy: http://www.youtube.com/user/lindybeige#p/u/76/hqtp08ZSAYE although he does rant about a lot of other stuff, and can be very opinionated, but his vids on medieval armour and weapons are good)