The other day, I started releasing my core Java development library, under the name ckkl-core, as an open source project. For that I had to decide on a license and so I asked for the opinions of friends and the open source community in Greece. Combining these with my own findings, here is a list with helpful URLs:
David Wheeler has prepared a nice slide depicting the relationship between several open source licenses. His opinion is that one should go for a GPL-compatible license.
The Software Freedom Law Center, suggest the way to Maintaining Permissive-Licensed Files in a GPL-Licensed Project.
This article (with a second part) explains how to pick an open source license.
You can also try the License Wizard. The first page user interface is a little awkward. Choose Yes, or go directly to the second page 
Also, take a look at this quick reference. I find of particular importance their comment:
The most common misunderstanding about software licences is that giving someone else a copy of your source code under a licence restricts what you are allowed to do with your source code. The truth is, if you write some code, and give it to someone else under the terms of Licence X, or publish it so that anyone may use it under the terms of Licence X, that this does not subject you to the terms of Licence X! You are the author of the code, and you hold the copyright, and giving someone permission to use the code does not restrict you to using the code in only the way that they are allowed to use it!
And, of course, you should read what GNU has to say.
By the way, I have chosen the Apache License Version 2.0 for ckkl-core which is:
a collection of Java classes developed for personal projects and research. Its implemented features include but are not limited to Java type handling with aliases and equality testing, easy discovery and accessors for JavaBeans properties, functional-oriented collections (list with map(), filter(), and others), and an API to support an easy toString() implementation even for the most complex cases.
Over the years I have developed a library of, let’s say, personal taste; a library which is my swiss army knife when looking into some new (research) idea. Something I use in order not to re-invent the wheel every time. The source code is currently heavily undocumented and I will be releasing new versions as soon as I can put it into some “eye-friendly” shape (javadocs included). I will do my best on that, time permitting. So, stay tuned !
