My favourite comic books currently are Disney comics (particularly Uncle Scrooge---my favourite creators are Don Rosa, William Van Horn, and Carl Barks), Asterix, Tintin, Lucky Luke, Iznogoud, and Spawn. Spawn is the only comic book series that I like that can be considered "mainstream" today, i.e., the superhero kind. I also like comic books like Phantom and Zorro, but I've not been able to read them in years. While these comic books are my absolute favourites, I enjoy comic books like the Spiderman series, MAD, Archie, Fantastic Four, the Superman series (at times), the Batman series (at times), The Spectre, the whole Adam Warlock/Infinity Gems series, Silver Surfer, Venom, etc. A more recent discovery of mine has been the Bone comic book series which I find to be excellent.
I consider comic books to have played a really big role in where I am today, in terms of science, philosophy, and music. I consider comic books to be highly educational, inspirational, and, since I don't have a better to word to describe it, "genius extractors" (i.e., they bring out the best in a person). In fact, a friend of mine just pointed out to me that there's a correlation between "intellectuals" and comic book readers. A lot of the comic books I enjoy portray an amalgamation of characters who could be called "renaissance people". While I enjoy novels and have read many in my time, I consider the graphic novel to be the best form of literature that exists today.
To end on a more negative and whimsical note, the comic book as a form of entertainment is dead. The primary reason I think is just progress. Just like comic books replaced some other form of entertainment for the kids (say the Tom Sawyer/Huck Finn type of adventuring), video games and the Internet are replacing (have replaced) comic books.