Ajaxian (http://ajaxian.com) is a decent one for the JavaScript / DOM manipulation side of things.

A List Apart (http://www.alistapart.com) is great.

Read Write Web (http://www.readwriteweb.com) has a good selection of articles and news.

Paul Irish posted a list of about 200 front end development blogs that he follows. His post is the best answer I can think of to this question.

http://paulirish.com/2010/front-...

Update: Paul recently published an updated list. There are now two feed collections: one for front end development (258 feeds) and one for standards and browser development (49 feeds).

http://paulirish.com/2011/web-br...

I can never recommend [456bereastreet] enough. Roger might be the very person that gave me the knowledge I needed to get to where I am today. Even his older articles are still a worthwhile read.

[456bereastreet]: http://456bereastreet.com/

I also track reddit sub groups and find they are a great source of info:
http://www.reddit.com/r/javascript/
http://www.reddit.com/r/web_design/

I like how posted content doesn't have to end with the original author as the authority, everything is open to discussion.

Css Tricks http://css-tricks.com/
Tips, tricks, insights. Go here on a regular basis to learn and keep up.

Css Wizardry http://csswizardry.com/
Not as many posts recently, but very thoughtful and smart posts over the past couple of years. Worth reading through.

Filament Group Lab http://filamentgroup.com/lab/
Called 'lab' but mainly a blog or at least place with lots of great articles. These guys are great.

A List Apart http://www.alistapart.com
Venerable and still going strong.

Impressive Webs Impressive Webs

Mobify Blog http://www.mobify.com/blog/
Responsive web design posts, how-to pieces, thoughts

HTML5 Doctor http://html5doctor.com/

Position Absolute http://www.position-absolute.com/

Webkitbits http://www.webkitbits.com/
Blog about the engine behind Safari, Chrome, etc.

Newsletters. The questioner didn't ask for this, but to my mind these are some of the best resources out there for keeping up. The folks behind these newsletters do a ton of work keeping up with the latest best posts so you don't have to do as much searching around.

CSS-Weekly http://css-weekly.com/

Responsive Design Newsletter http://responsivedesignweekly.com/

Web Design Weekly http://web-design-weekly.com/

HTML5 Weekly http://html5weekly.com/

Podcasts. Don't forget to check out podcasts as well. Best I've found is Shop Talk Show: http://shoptalkshow.com/

I will concur with most of what other people have said

A List Apart has great articles. Ajaxian was great until they lost their editors to palm.. now it seems to have fallen off. Smashing Magazine has nice articles especially if you are more into design or are just starting working on front end development.

A couple blogs not mentioned nettuts+ (http://net.tutsplus.com/) has great articles and useful video quick tips.

There is also some great JS dev writing on Ben Cherry's adequately good (http://www.adequatelygood.com/)

Web performance is a huge part of front end development, the ultimate blog for which would be Planet Performance, an aggregator of curated web performance blogs.

I follow those blogs:

Web Design, Development and Graphic Design Resources
Web Design and Development Magazine
Codrops
Smashing Magazine
Web development tutorials, from beginner to advanced
In-depth tutorials and articles on web design
Design Tips, Tutorials and Inspiration
For Web Designers and Developers
Dzyngiri | Online Design Magazine
For People Who Make Websites

Many of my favorites are already mentioned, but

CSS tricks (http://css-tricks.com/) has good video tutorials

I've learned forward thinking front-end techniques via http://www.impressivewebs.com/