The Illuminatus Trilogy did a lot of heavy lifting in inspiring a sense of meta-skeptical relativism, though largely by offering a central hub for many other rabbit holes.

Gurren Lagann instilled me with a sense of inextinguishable optimistic determination, for myself individually and as a part of the human race

There are plenty of others, but these two had the most profound effects.

Edit: I almost forgot about this webcomic that lived in the back of my brain until I got a bidet.