Bone
This was recently released in a complete, epic-sized volume containing the entire series. Priced very reasonably at $40.00. I know I sound like shill for Jeff Smith, but if there ever was a time to get into Bone, right fucking now is sounding pretty good. Not only that, Bone is appropriate for most any age.
Kingdom Come
Kingdom Come, being an amazing work of masterful storytelling cimbined with amazing, eye-grabbing artwork, is one of my favorite comics. I always kind of felt like you needed to know certain events/things/people from DC Comics history, however. Kind of like, it's tough to understand just what is going on early in the comic if you don't know why everyone should be afraid of Captain Marvel/Billy Batson.