At LinkedIn, we have our own JSP Compiler. Our version of JSP is more like FreeMarker than JSP since it solves many of the deficiencies of JSP. Since we allow a different syntax than standard JSP (more powerful EL, new tags for looping, loading from classpath), we (like FreeMarker) don't get much love from IDEs.
We don't get much in the way of syntax-highlighting or code completion. However, since we use JavaCC/JJTree for parsing, I'm wondering if Eclipse or IDEA (or even NetBeans) allows replacing the default syntax definition with a new one.
Has anyone extended one of these IDEs to enhance its JSP syntax highlighting and compilation? If so, I'd love to hear about it. If not, it's likely we'll be doing it in the near future.