There are plenty of cool ones, and I thought I'd mention a couple of my favs that I don't think many people know about or have seen.
I haven't been a big fan of the Magical Girl genre, I'm not the target audience after all, but I really liked Magical Girl Lyrical Nanoha because its like a regular magical girl series, only the action is much better and had some great attacks. My favorite has to be main character Nanoha
s Divine Buster:
http://www.youtube.com/watch?v=qBunw-BxydQ
Another favorite of mine is the finishing sequence from the mecha series Godannar, called the Soul Breaker. Starts out by punching into the enemy, releasing something that freeze it, finish it up with a high jump and following kick that goes straight through the monsters.
I'm also a big fan of One Piece and I like Zoros fighting style. There are to many attacks to mention just one, so lets just say I'm a big fan of the santoryu sword style in general. I remeraber liking the Gazami Dori attack he used against Mr1 for some reason, hard to say why but its simple yet cool looking. I know more people have seen One Piece then Nanoha and Godannar though.
And while on the subject of iconic attacks, this isn't anime, but I just have to mention the Rider Kick attacks from the Kamen Rider series:
http://www.youtube.com/watch?v=tpZi687QdIQ
http://www.youtube.com/watch?v=jbnKqqlHkvs