Wikipedia is hands-down my most visited webpage. I look up TV shows while I'm watching them (and inevitably get spoiled). I live for discovering a page with a title that starts "List of..." I look up stuff I know because I'm never sure that I'm remembering it correctly. I look up stuff I know just to learn more. Some recent faves:
Time formatting and storage bugs
Beginning 14 September 30,828, Windows will not accept dates beyond this day and on startup, it will display an error regarding "invalid system time" in NTFS. This is because the FILETIME value in Windows, which is a 64-bit value corresponding to the number of 100-nanosecond intervals since 1 January 1601, 00:00:00.0000000 UTC, will overflow its maximum possible value on that day at 02:48:05.4775808 UTC.
Warn your great x n grandkids.
I like to dip into this list every once in a while. I still haven't read the whole thing, but I have corrected some ideas I believed to be true. The best part, tho, is I've learned about dumb shit that other people believed (my blessed facts versus their barbarous trivia).
I've been teaching "Proposal," so I've had this page open in a tab just for reference, and each time I look, I learn something new. It's a surprisingly comprehensive page. Sometimes you'll look up something you consider well-known, but find just a few paragraphs, and wish for more. This page is a delightful onion of facts and references.
List of lists of lists: This article itself is a list of lists, so it contains itself (see recursion)
Does what it says on the box. To be quite honest, I just put "list of lists" in the search box not actually expecting to find it. What a treasure trove. Make a pot of tea and settle in.
A list of words which don't exist in common usage outside of an idiom. I come across so many of these as an English teacher, when a student asks how to write a sentence using a newly-learned word, and all I can think of is a single example because there's just one way we say it.
(If you liked this blog post, you'll love Erin McKean's newsletter, Things Learned While Looking Up Other Things. It comes out tomorrow.)