Following are some random, interesting places I've been to. Note that some of these places may cause sanity slippage, PROMOTIONS, randomly moving objects in your peripheral vision and mushrooms to sing a samba for you. Please read the description before jumping into the unknown depths of the internet.
Lainchan. A cyberpunk-themed imageboard. It's safe for work. I think. Requires being mature to view.
Textfiles. Internets history, pre-historic era(19XX) to Late NeoBBSic era (2005).
The first website. Essential for any website list.
Look at hentai pics like it was the early 2000s!. It goes without saying that it's NSFW.
ZOMG TEH REI I've been following the 0x40hues folks for a while but this is the first one I listened to.
Civilization fansite The writeups are a good way to spend a night. Some misc stuff too.
Anime gifs! Last updated in 2003...