The best fight scene/rivalry you have seen in a anime

[Def_March]

the ulitimate face off is vegeta`s glalik gun vs goku`s kamahameha. good times  

[Def_March]

Mugengod

Demon Lili

bored_silent_boy

Black Star VS Mifune the body guard in Baba Yaga Castle

hey....that was the same one i was going to type. lol

anyway that one, along with...

Ace vs Black Beard (One Piece)
Lee vs Kimmimaru (Naruto)
Lee vs Gaara (Naruto)
Naruto vs Sasuke (Naruto)
Agito vs Akira (Air Gear)

and much much more!!

she pretty much nailed mine. although i would add:

Mustang vs Lust (FMA: Brother Hood)
Edward vs Envy (FMA)
Armstrong vs Scar (FMA)
Edward vs Father (FMA: Brother Hood)
Ichigo vs Aizen (Bleach)

that's all so far!!

so your Fullmetal fan right?