If you are using Ant, you owe it to yourself to check out Ant-contrib, a great collection of really useful tasks that make writing highly functional Ant scripts a snap.

For example, there's a <if> task that lets you write in conditional logic, like this:

<if>
  <equals arg1="${target}" arg2="windows" />
  <then>
    <antcall target="build-windows"/>
  </then>
  <else>
    <antcall target="build-solaris"/>
  </else>
</if>

As you can see, the <if> task supports <else> conditions, and also supports <elseif>.  It can test on any condition that Ant's built-in <condition> task can, such as equality, the availability of a property, whether file(s) are up to date, even if a document is available via an http request.