I am considering starting an OSS project and would like some advice.
I would like to use a licence that allows free use of the project for personal and non-profit use but would allow me to charge for a commercial licence (like or similar to http://www.extjs.com/company/dual.php).
Could someone please advise or link to some articles on how to approach this? Thanks in advance.
As the Open-Source-definition describes, you cannot limit the usage of your project, if you want to stay open-source. In other words: you cannot forbid a commercial use for an open-source-app. So you can choose another (non-open-source) license, that fulfills your demands, or you choose another way.
One possibility is to release only the source under open-source-license and have another license for binary distributions. As far as I know thats true for Java. That works good, if the build of your app is somewhat complicated.
You can release your app under the GPL-license. That does not forbid commercial use. But if some derivate work is created, it has to be GPL-licensed too. That works well for libraries or similar stuff that isn't used alone, but in a merged product. EDIT: As DrJokepu mentions, using a GPL-framework in a webserver-stack would help to avoid to release your own sources. That's why one extension to the GPL is the Affero GPL, that need you to release your work under the same license (AGPL) even if you don't release it, but only use it to build a public webpage. So for webservices you need the AGPL to achieve the same result.
You can't us an OSI-certified Open Source license and ban commercial use.
If what you want to do is stop somebody from taking your software and selling their version as some sort of shrink-wrapped software, you can use a GPL-style license. For maximum compatibility, I'd recommend GPLv2+ (Gnu General Public License, version 2, or any later version at your discretion). With that license, somebody can sell your software, but they have to make it clear that anybody can get the source, and that it can be freely redistributed. That would, I think, cover most of what people want to ban as commercial use.
The producing open-source software book has a great section on dual licensing. It outlines the approach where a single entity, such as a foundation "owns" the copyright to a projects source.
The foundation chooses to make the source available under two different licensing schemes, one closed and another that is open-source. For your particular case you will want to ensure that you stick with a strong copyleft license (i.e. such as GPL) to prevent commercial derivative works of the freely available source code.
However, as others have noted, this does not prevent commercial entities from using your software, just from taking your work and selling it to others. In some cases this works out, as strangely enough, many organisations would rather purchase something than download and use something for free. These are the same sorts of organisations that need legally binding contracts with vendors and some form of support. I.e. When you sell software you are actually selling a whole bunch of other services at the same time as a "shrink wrapped" product.
Now, how can code be kept closed and sold, as well as released under the GPL license? The mind bending legal part of the whole arrangement, is that contributions of IP to the foundation are not made under the GPL license. Rather, developers give their IP to the foundation under "contributor agreements" which pass on copyright of their changes to the foundation and permit the foundation to release the code under two different licenses. This last little caveat is the big downside to dual licensing, sometimes developers are not interested in contributor agreements, they want there changes only available under the open-source license and nothing else. Quite a few contributor agreements that kick around the place, but here is the one that sun uses for MySQL.