Most examples are included in the documentation manuals for each module comprising the JBoss Transactions code base. A couple of modules provide sample applications outside the manual. To access the examples either get the transactions code from source code repository or download a release distribution.
http://www.jboss.org/jbosstm/downloads.html Downloading the latest release distribution (JBossTS 4.9.0.GA) will get you started quickly.
Inside each release distribution are several modules. Each module contains several manuals targeted for an audience. The "Programmers Guide" contains code examples along with explanations of context and theoretical background.
The Transactional Web Services (XTS) and Transactional Bridging modules provide example demonstration applications.
Depending on the type of example you are looking for this is what you can expect to find.
Java POJO example. Providing transactional (persistent, atomic) behaviour to a plain old Java object. page 14, 25, 38. - ArjunaCore -
JTA example. page 33 - ArjunaJTA -
JTS transaction propagation. page 68 - ArjunaJTS -
Transactional Web Services. Sample web application. - XTS -
Integrating JTA and XTS Web Services using a Transactional bridge. Sample web application. - TXBridge -
That should keep you going for a while
If your looking for EJB3 examples try visiting the JBoss EJB3 project.