Here's a few that I can't believe haven't been mentioned!
(just being thourough here)
The Lance Longinus from Evangelion.
The Mass Production Eva's Blades, also from Evangelion.
The Lazer Cannon that Kinada picks up in Akira.
Ukiyo's Spatula (pick a size) from Ranma 1/2.
Ryoga's umbrella from Ranma 1/2.
Cologne's staff from Ranma 1/2 (would be insane if it were to scale!)
Lu Bu's Lance, Sky Scorcher, from the Dynasty Warriors games (there was an anime too ya know!).
Guan Yu's Halber, Blue Moon Dragon, from Dynasty Warriors.
A lot of the other
signature weapons from Dynasty Warriors are really nice looking but these the best. Though I think that the oxe head club of Xu Zhu, , would be incredible to make!
The variety of awesome weapons from the Soul Calibur series. I'd pick one but I don't follow the series.
Honorable Mention:
Edward's Stinky Gas guns from Cowboy Bebop.