Zanbato: Japanese anime style sword.
The style of greatsword from japanese animation and manga is called a Zanbato, which supposedly translates to "horse slaying sword." Unlike more realistic great swords like the odachi, zwiehander or claymore, the weapons featured in anime usually have really thick blades, and at least as long as the one who uses it is tall.
I am suggesting a sword similar in shape to the Thinkgeek Titan sword. Unfortunately the Titan is not made for LARP. Some iconic zanbato swords include: Zabuza's sword from "Naruto", and Cloud's buster sword from "Final Fantasy".
While I have seen other entries for a similar idea, I wanted to post something a little more specific. I'm thinking of a sword 6-7 feet long, with a very wide blade. The sword by think geek looks to have sold very well, so something of a similar style, made with the durability of a Calimacil would probably sell extremely well also. I'll provide some images of the general style: http://m.cdn.blog.hu/kh/khaos/image/narutohun/zanbato.jpg
here is one that someone made: http://drentha.com/images/photos/2007-06-16/IMG_2772.JPG
and here is an example of size: http://media.animevice.com/uploads/0/5783/235446-k_fighting_z_super.jpg
and here is the thinkgeek sword: http://laughingsquid.com/wp-content/uploads/f22f_foam_titan_sword.jpg