Links! People used to put lists of links to other sites on their sites back in the day. (Or so I've been told, I wasn't alive in the 90s.)
Here's a list of sites in no particular order that I think are worth looking at. Some you probably know, some you might not. I hope you discover something new!
xkcd - The iconic, sometimes science, sometimes surreal themed webcomic.
Sulla's Website - An excellent essayist on Civilization and other games.
E.B.O.N.Y. Riddle Game - The weirdest (and best!) riddle game on the internet. Incredibly esoteric.
Ze?t - Another online riddle game. I don't like it as much as E.B.O.N.Y. but it's still worth your while if you like hard puzzles.
The Language Construction Kit - A fantastic guide to creating languages.
Enigma - An old, free puzzle game about marbles and matching colors.