Since I started working I go to StackOverflow for everything. But as we all know it is good to have many ways to skin a cat. where is your other favorite website to visit for programming Reference?
I hit up the documentations of whatever languages I happen to be using.
Twitter, I follow a bunch of fellow programmers and muckity-mucks in the programming world.
When I start using a framework / library, I always have a look at how their documentation is ; if it's looking fine, it becomes a "reference" I tend to check before anything else. (Well, that's when I'm not one of those who whoose using that framework/library ; else, quality of the documentation generaly is a criteria of choice)
For instance, in PHP, you just have to go to php.net/function_name
(like, for instance php.net/in_array) to get documentation of a function -- that's really useful.
(And there are often user-notes at the bottom of the page, which can be quite helpful to help solving common problems)
Then, google is often my friend ^^
Google is a great resource obviously. But with google knowing how to ask the right question is half of the battle.
And a lot of times documentation comes with the selected technology you are working with.
Recently I've fallen in love with the Apple Developer Center for all the great guides, and documentation they provide.
Also MSDN for .net.
For Flash the Documentation is good, and actionscript help and tuts gotoandplay. (Game specific-ish)
Not a website, but as a general series of succint reference books, I like the O'Reily "Pocket Reference" books.
Duplicate maybe?
http://stackoverflow.com/questions/392993/what-are-your-favorite-programming-bookmarks
http://code.google.com/, for everything else there is always Code Complete!
Gotapi.com is so important. It's got online documentation for many languages with a slick search system. Try it out.
For technical questions the "official" IRC(Internet Relay Chat) channel of the technology/language I am using. I have learned so much from IRC it is unbelievable.
I go to the official programming reference/manual of X. Like PHP -> php.net, jquery -> docs.jquery.com, rails -> api.rubyonrails.org.