This really should go in the comic book question thread
I don't know which Deadpool graphic novels to buy but I can recommend Cable and Deadpool volume 2 called "The burnt offering."
As for individual issues I recommend the last storyline of Deadpool's series called "Healing Factor." I also recommend the Storyline "Deadpool, agent of Weapon X."
Here is the Deadpool respect thread. Some of his feats here come from the story-lines I mentioned..........
http://www.killermovies.com/forums/f95/t380685.html
If you like Deadpool then you will also like Agent X. He is a mercenary just like Deadpool (He has a healing factor and makes jokes.) but his series only lasted 15 issues. If your interested you can see some of his feats in the respect thread I created for him here............
http://www.killermovies.com/forums/f95/t411899.html