Since it seems to have become the standard I'll give a webcomic outside of Tapastic as well as a hard copy.
Girls With Slingshots by Danielle Corsetto. This webcomic got me into this world of comics. I had a lot of trouble getting into the digital format of comics, but this in a sense was the cherry breaker. It isn't like I didn't try others before hand (VG Cats and Penny Arcade) Just none of them held my interest till this one. And, I have found more great comics just by continuing to follow her.
Blankets by Craig Thompson. I've always enjoyed comics. Superheroes, Sunday strips, and of course Calvin and Hobbes. But, this book is what I aspire to be. All comic's require artistic talent, but in my opinion this one shines brightly over everything else.