With IntelliJ IDEA 9.0.2 you can enjoy editing web.xml with the new initial parameters support. IntelliJ IDEA now collects parameter names and is also aware of parameter values types. This allows the IDE to generate (with Alt-Insert), complete, highlight and validate them appropriately.
Grab the latest EAP of IntelliJ IDEA 9.0.2 to try it today.
If you are a plugin writer, you can provide your specific context parameters through the special
com.intellij.javaee.model.xml.converters.ContextParamsProvider extention point.