Comic Trade-paperbacks/graphic novels for beginners?

I am a 15 year old girl and have always had a fondness for the film adaptations of clic comics, Spiderman and Superman being favourites. I am a complete amateur fan so please forgive my limited knowledge of the subject. I have read very few graphic novels, the only ones I have read and thouroughly enjoyed are Watchmen, Kick-*** and Ghost World. I really like Zombie related stories as well as the typical superhero genre. I also read a few manga series such as D.Gray Man, Death Note and a couple of Shojo series. My apologies for not being able to give many references to past experiences with the relevent medium. But if you could help me with some recommendations based on some of the graphic novels/films I have enjoyed in the past it would be greatly appreciated.