The Spring MVC Framework offers a simple interface based infrastructure for handing web MVC architectures. In most cases a Spring MVC application is quite testable because Spring does not require the developer to extend a base abstract actions/controllers a la Struts.
There are many other Java-based web frameworks out there (Struts, WebWork, various JSF implementations, Tapestry, etc.) and all have their pros and cons, but if you are already using the Spring Framework for other services, an added benefit of using Spring MVC is that other Spring Beans can be easily injected into the web controllers. If your services injected into your controllers are interfaces, it is then very easy to write alternate simple implementations of those interfaces for the purpose of testing your Controllers.