Is there a simple way to have your "Service Layer" deployed separately from your web layer, so that I can reduce the number of times per week that I have to, package, build and deploy the entire WAR file?
I'm using Tomcat mostly, but I'm hoping for something more generic to Java web servers
You could move your "service layer" to a second application and have the front-end application communicate with the "services" using some sort of remoting technology.
Spring Remoting (a.k.a. HttpInvoker) makes this very simple to use.
If the package-build-deploy process is necessary, but heavyweight enough that you want to minimize or avoid it, you might also consider making that process easier, faster, or more automated.