Seasonal and regional, but whenever there is a hint of snow in western Washington state, I start reading posts by a UW meteorological professor: http://cliffmass.blogspot.com. He's acutely focused on the "perfect storm" of conditions needed for any significant amount of snow in our region.
Before I moved to Texas I followed Cliff almost daily for new posts. He was especially detailed when any "pineapple express" or snow storms would come along. Way more useful info than komo4/king5/etc.
I have been fascinated for many years by the website of math professor and puzzle-maker Erich Friedman; I can still spend hours looking at the optimizations of interesting packing problems.
http://www.metafilter.com a discussion site that charges a one time fee for accounts and has paid moderators. Works brilliantly, except that they deserve more money.
http://www.fonerbooks.com - because of the "content first" design, and because its demise was caused by a major change in the Google search algo that promotes social media hype and interaction more than readable and valuable information. It has been an inspiration for many years.
My own product that I built 7 years ago. I visit it every single day. Built as one individual from everything - SEO, Sales, Lead, PM, Development, QA, Product-website
Physics: http://www.asimmetrie.it - http://www.smartfish.ch
Cyberpunk: https://www.neondystopia.com
Computing: https://calomel.org - https://www.michaelwlucas.com
I particularly enjoyed the clever presentation of the concept design @[http://www.smartfish.ch/file/SmartFish_Design_10.wmv] and the total overwhelming hilarity of Michael @[https://www.michaelwlucas.com/autobiography/the-porn-star].