1. Smashing Magazine

This site posts, what I believe, is the best array of useful, diverse articles for developers, designers, content managers, SEO “gurus,” and even photographers.  Most of the information is aimed at developers and designers, and it lacks significant Flash/Flex resources, but it’s definitely worth checking out.

New articles are posted daily.

2. Kuler

This site has received a lot of praise from the design community as of late, and it’s easy to see why. Kuler is an online application that helps you generate new color schemes – or you can adopt one that’s already been created. You can browse by theme, popularity, or just discover new schemes randomly. You can also use their Pulse tool to view trends on the site.

Not a bad tool for a bunch of lazy developers.

3. Curtis Morley

This one is for the Flash and Flex developers out there.  Curtis has a number of great articles, but if you starting out (or even if you’re an intermediate AS3 developer), you have, no doubt, run into a number of different errors.  His site is littered with common errors and he usually has multiple solutions to them. If you have an error that’s had you banging your head on your desk the past few days, chances are the answer lies somewhere on this site.  Not only do his articles cover possible solutions, user comments are often contain problems and solutions and he responds frequently.  

I probably owe him a few days of saved problem solving. His main blog is linked above; if you’re looking specifically for the Flash error messages, click here.

4. W3Schools

W3Schools might be the best site to visit when learning a new language. You can find everything from HTML (including a separate HTML5 section), to JavaScript, to SQL. One of the best features of this site (besides being free) is their “Try It Yourself” editor, which lets you learn the language by doing, rather than seeing.

And who can’t use a new language to put on their resume?

5. Google

I know, I’m not exactly breaking news by shouting about Google’s usefulness. But by typing almost any question, problem, or error into Google, not only will your question probably be answered in the first dozen or so results, but you might just stumble onto a useful site that you didn’t know existed. Then one day you’ll create your own article about useful sites for designers and developers.

By the way, this doesn’t even cover all the tools available, such as Google’s conversions, translations, and, of course, Google Analytics.