I'm sure there are some out there, but the only standalone JSP compiler I'm aware of comes with BEA WebLogic Server, which is an expensive commercial J2EE app server.
Why don't you run the JSP container locally on your development machine, editing your content (files) within the web app's document root directory?
The other thing that comes to mind (which I don't have much experience with) is HTTP-based unit testing. Check out Apache Jakarta's Cactus framework and see if it fits your needs.