Sheldon Brown's Articles
sheldonbrown.com
sheldonbrown.com
Especially good information on practical fixed gears and three speed hubs.
Before he passed, I sent an e-mail asking a few questions and Sheldon responded personally, with fairly detailed responses. It was pretty rad.
There's a lot of really useful information on there.
Some of my favorite parts.
The three speed hub with a fixed gear: http://sheldonbrown.com/asc.html
The section on frame fit (semi controversial topic depending on the crowd): http://sheldonbrown.com/frame-sizing.html
I've thought it'd be neat to turn the site into a wiki that can be maintained by bicycle enthusiasts.
edit: just found this whole page on brand mismatching, written by John Allen on the site in 2011, so there is someone doing updates. http://sheldonbrown.com/drivetrain-mixing.shtml
more edit: @zecho notes that family, friends, and bike shop are updating the site
i'm using a lot the bicycle site at stackexchange. granted that most answers are just pointers to sheldon's site for now :)
I like to use his gear calculator to remind me why I spin out on the top end: http://sheldonbrown.com/gears/index.html
http://sheldonbrown.com/pedals.html (scroll down to "Pedal Threading")
I also loved imagining people's left pedals falling out, until it happened to me (well, it was the right). Make sure you screw your pedals in tight!
Brown's in particular is full of personality, not only in his writing, but in the layouts, color choices, photo choices, quotes, et cetera.
I also have benefitted from many hours spent reading through Brown's site. What a great resource and gift.
Sheldon was married to Harriet Fell, my finite state automata professor. I think she's doing some of the page maintenance.
1) He's practical to a fault -- he doesn't delude himself or others
2) He's extremely generous with his knowledge.
Anybody from any profession can take a lesson from his life.
RIP Sheldon Brown.
In addition to the incredible depth of very practical info, the fact that his site exists is a demonstration of what the pre-commercial web was all about: 1 guy contributing knowledge for the benefit of many others, giving time/effort for the greater good.
Never met him, but i miss him.
I never met Sheldon but he has been and will continue to be my go-to person for bike advice. Whenever I'm fixing my brakes and have to take a minute to think about mechanical advantage, I think of Sheldon. I'm very thankful for his efforts and the ongoing efforts of the people who maintain his site.
Was a sad day when he passed.
Thanks to Sheldon my bike workshop grows and grows and I basically can do all aspects of bike maintenance myself.
He's a true DIY pioneer for real!
His cycling in France articles were a pleasure to read.