Jar works with standalone Hadoop, but not on the actual cluster (java.lang.ClassNotFoundException: org.jfree.data.xy.XYDataset)
Java can not use jars that are in other jar:/ (classloaders can't handle this)
So what you have to do is to install those packages separately on each machine in cluster, or if not possible add jars on the run, to do this you have to add option -libjars mylib.jar when running hadoop jar myjar.jar -libjars mylib.jar and this should work.
Wojtek's answer is correct. Using -libjars will put your external jars in the distributed cache and make them available to all of your Hadoop nodes.
However, if your external jars are not changing frequently, you may find it more convenient to copy the jar files to the node's hadoop/lib manually. Once you restart Hadoop your external jar will be added to the classpath of your jobs.