Well I'm not a big anime guy, usually only watching the ones you'd expect. But I've tried to narrow it down to one anime per type. Here goes nothing:
1. Jackie Chun vs Goku: Barring the Ape incident and Roshi sorta cheap shotting Goku at the end due to his shorter legs, I love this fight. It kinda shows how much better DB fights are the DBZ fights, even if they aren't doing as much crazy stuff. It was close and entertaining. If I could remember more fights from Dragon Ball, this one might change but I remember this one the most and I suppose it just left an impression. All I can say.
2. Luffy vs Crocodile: I stopped reading One Piece after this(I was clearly out of my mind) but it didn't change the fact that it was awesome. Luffy absolutely, refused to die! Crocidle basically leaves him ****ed 2 times, and Luffy keeps coming back for more. I need read the rest of One Piece. It was sooo good.....
3. A tie. Near vs Light, and Yami vs Noah. The first one comes into play because I like Near. I really do. And I dislike Light. So when Near put him in his place, I liked it. But that doesn't change the fact the Near got so ****ing lucky in those last few chapters.
As for the second one....
http://www.youtube.com/watch?v=quRscpyrM5w
Look at 5:32 to 5:42. Listen at 6:09. And now go to 8:03 and watch the rest to see dueling at its finest.
4. A Naruto fight actually. Sasori vs Chiyo and Sakura: I don't know why, but I like this fight a lot. Chiyo and Sakura have not known each other long but they recognize the need for each other because their opponent is stronger than them separately. I like how Chiyo gives Sakura some respect in the fight, whereas Kakashi would likely have told her to GTFO. It was a nice fight, not much more to add. Usopp and Chopper get an honorable mention though when they fought the Mr. 4 team. Was cool.
5. The Clone Wars....in Pokemon. I'm of course referring to Clones vs the Originals, and Mew vs Mewtwo. Would have been cool if Mewtow had let the Pokemon fight normally instead of blocking their powers but, hey, what can you do? The other Pokemon made up the raw part(Pikachu in particular took quite a beating) and the Mew duo made up the power part. The world was still in a raging storm at the time so it was very epic.
6. I'm torn but I have to give it to Gohan vs Cell. I can't help it. Gohan was my favorite and to see him become the biggest badass in the series at the time was so awesome to me. Cell is cool too and one of my favorite villains from DBZ. And the final Kamehameha battle was just awesome, especially with Gohan using only one arm. It was badass to me as a kid and it is now.