@Tank252ca:
Some people have mentioned spears and pole arms, but those are a general class of weapon. There are many variations on pole arms and spears. Spears typically have a double edge, and pole arms often have the spear head flanked by double or single axe heads, so I did a bit of research on Wikipedia. What makes Whitebeard's weapon stand out is the lack of an axe head and the single sided blade, effectively making it a sword blade on a pole. So my conclusion is that Whitebeard is wielding a Japanese "naginata". The European equivalent would be a glaive.
http://en.wikipedia.org/wiki/Naginata
What is interesting is that Oda chose to give Whitebeard a weapon that, according to Wikipedia, has become associated with women and in modern Japan is studied more by women than men.
Wrong, as you can see Naginatas blade is like a katana, small, and Whitebeards blade isnt small, so it is probably a guan dao/ Kwan dao, the famous weapon that the warlord Guan Yu used.
http://en.wikipedia.org/wiki/Kwandao
This does acttually fitt very weel, as they said Guan Yu was the most famous warriors at his time in China, kinda like Whitebeard now.
I hope though that we will see a strong female with a naginata… That would rock...
EDIT:
And you have wrong on another point as well, spear is a polearm, just like sabre and katanas are swords. Polearms are spears, glaives, pikes, halbeards, lances, naginatas, Yaris, qiangs, Guan daos and so on.. understand? 
I'm a weapon nerd... ^^