Mikhail Tal was unanaimously THE greatest attacker in the history of chess. Whereas others sought to utilize tactics in their games, he created the conditions neccessary for their introduction. He was an absolute marvel!
Even though his attacks may have been unsound at times, which doesn't matter as much as some might think, they usually involved deep thinking and calculation. Thus, his attacks weren't sporadic, meaningless charges into the unknown. They were calculated, magnificent strikes into the enemy camp.
As two close seconds, I'd have to say that Alekhine and Kasparov were both excellent attackers as well. Alekhine is always going to be at the top of my collection for annotated games.
It's hard to take issue with the choice of Tal.
Among the slightly lesser mortals, anyone familiar with Emory Tate?