I think Jim Lee is one these artists that really doesn't need any presentations. If you already read some of the DC, Marvel or Wildstorm comics from the 80's to nowadays, you probably stumbled with some of his covers and pages. In my point of view, he's the best penciller that ever worked for these major companies, a truly master of his tools, always pushing further on style and concept.
You can see some more artworks form Jim Lee at his Comic Art Community Profile or at his DevianArt.
Dan Adkins is one of the legends of the silver age of comic books, being a penciler and inker for almost every big comic company. He's one of the responsibles for defining the Science Fiction and Fantasy comics artwork, with a really remarkable and clean trace.
Unfortunately, Dan Adkins don't have a Official Website, but you can see more of his work If you search on Tumblr and you can know more about his story at his Wikipedia profile.
Praised by some, hated by others, Rob Liefeld is one of those comic book artist that you should love or leave. Anyway, what made me brought this artist here is because of his major influence on the 90's comics, Rob style displays totally the techniques that were developed on this period of comics.
Dashed lines, horizontal panels, flat multi color covers, extreme muscle bodies, big high-tech guns. All this is quite familiar for anyone who read a comic during the 90's, what brings me some nostalgia.