Please reply with just one blog per answer to allow the voting system to bring the best/most popular to the top.
Even if you don't listen to The Java Posse [1] then reading the blog is great for a regular summary of what's happening in the Java world. But you should listen to the podcast :)
[1] http://javaposse.com/I got a lot of my java dose from http://java.dzone.com (previously Javalobby.org)
In no particular order and I'll try to not repeat any previously mentioned. I've noticed that most blogs have been 'consumed' by news sites. So you will be in good shape if you grab the feed from 3-4 of these aggregators rather than piecing them together one by one.
On Java [3] (O'Reilly)
The Server Side [4]
Dr Dobb's [5]
Artima Developer [6]
Java Crawl [7] - Java News Aggregator
Spring Source [10] (Rod Johnson)
JBoss Matrix [11]
JRoller [12]
Steve Yegge [13] - has some gems about programming interviews.
Reza Rahman's Blog [14] (EJB3 in Action Author)
[1] http://www.ibm.com/developerworks/javaJust a quick note to complete the previous answers:
[1] (Planet JDK) allows you pretty much to follow all of them ;) (almost)
http://www.theserverside.com/ is pretty good for JEE articles.
In addition to the blogs listed in the replies(above), there's also a very good Java podcast that you might want to subscribe to. It's called JavaPosse [1].
They talk about latest developments in all things Java( J2EE, J2ME etc ).
-Anup
[1] http://www.javaposse.comhttp://www.infoq.com/, http://www.dzone.com/, http://www.javablogs.com/, http://www.jroller.com/ and http://www.theserverside.com/ among many many others. The sites listed above aren't individual blogs but a group of aggregators with user submitted content.
These are more news-oriented sites, but may still be what you want:
For Java and a few others, anything by Bruce Eckel is going to be worth reading.
http://www.artima.com/weblogs/feeds/bloggers/beckel.rss
I took a look at what I am reading for java blogs and came up with this list
Java Weblogs [1] is a great place to start, lots and lots of java specific blogs.
Evan Summers [2] not posting very frequently.
James Gosling [3] Father of Java, but the blog is not technical, he is mostly involved with Real-Time Java now.
John Reynolds [4] more general programming/business type stuff
[1] http://weblogs.java.net/Dan Dyer's New Adventures in Software [1] is a great blog with quite a lot of Java content.
I don't want to duplicate infomation too much (DRY and all :), so see this answer [2] for a few more sentences about the virtues of the blog.
[1] http://blog.uncommons.org/Core Java Tech Tips [1] For in depth coverage on Java features (though updated less frequently)
[1] http://blogs.sun.com/CoreJavaTechTips/feed/entries/rssYou may find some Java core concept in http://webmoli.com blog.
http://www.mastertheboss.com has got plenty of tutorials about JBoss Hibernate Java EE technology.
Have a look at this blog -
Java Jazzle
[1]
This blog is work around technologies like spring and other java related techs.
If you read french check http://touilleur-express.fr A very good blog in french about java.
I can recommend DZone [1], which is basically Digg for Software Development. I subscribed to the Java Ta [2]g and there are a lot of good articles coming through DZone.
[1] http://www.dzone.comhttp://javablogs.com/ is another blog aggregation site.