The most expensive comic-book is a mint copy of DC's Action Comics Superman issue#1 by Jerry Siegel and Joe Shuster and published in 1938.
It was the first appearance of the modern super hero as we know it today.

It was sold in an online auction for US$ 2.1 million and the man that sold it was the actor Nicholas Cage, a huge fan of Superman himself.
This comic book was stolen from Cage's home 10 years ago but recovered again in April 2011, then sold in November.

It is said that there are only 100 copies of this comic in the world.

The comic book collection is very hot at the moment, the first issue of the Batman comic book was sold at $850,000 at the auction in May 2012.