All, I am starting with Spring and got the Spring 3.0.5 distribution. I see the following jars:
There is a following chart (from Diagram of Spring 3.0 module dependencies):

As you can see, there are several groups of modules:
"Core Spring" - context and its dependencies (asm is missed, aop depends on it)
Web
web - basic webapp integrationwebmvc (web.servlet) - Spring MVC Frameworkwebmvc-portlet (web.portlet) - Spring MVC for portletsweb.struts - Struts integrationData access
tx (transaction) - basic transaction supportjdbc - JDBC supportorm - ORM integration Other modules
context-support - integration with Quartz, Javamail, Ehcache, etcjms, oxm - JMS and object-XML mapping respectivelytest - for unit testingaspects - AspectJ intergration (usually not needed)instrument, instrument.tomcat - load-time weavingSo, if you use build tool that supports transitive dependencies (such as Maven), you usually only need to declare the required modules from web and data groups, and some from the other modules, if needed. Also you may need to declare context in order to configure logging.
For example, if you want to create a web application with Spring MVC and Hibernate, you declare webmvc (web.servlet) and orm. If you don't use Maven, you also need to import their transitive dependencies, as shown on the chart.
See also: