There is a fairly complete example of using ASM to generate byte code from a Java-like intermediate language in the implementation of CAL (a Haskell-like language for the JVM). If you download the sources at http://openquark.org/Open_Quark/Download.html
then you can find the code in AsmJavaByteCodeGenerator.java, and the java model classes in the same folder. The code generated is basically what javac would do, minus debug annotations.
The CAL implementation originally used BCEL but switched to ASM because ASM was significantly faster (probably an order of magnitude), and just as significantly, ASM is thread safe, so that concurrent compilation is possible, which is needed by CAL.
