Just compare the ScalaDoc of different Scala versions.
Things which come to mind (comparing roughly 2.8 (released 2010-07) to 2.11 (released 2013-03)):
Classes (just from the top-level scala.* package):
- Application
- Cell
- cloneable
- CountedIterator
- NotDefinedError
- NotNull
- Responder
- serializable
Complete packages:
- scala.actors and subpackages
- scala.collection.interfaces
- scala.concurrent (still exists, but its contents have been replaced completely)
- scala.dbc and subpackages
- scala.mobile
- scala.reflect.generic
- scala.swing and subpackages
- scala.testing
- scala.text
- scala.util.automata
- scala.util.continuations
- scala.util.grammar
- scala.util.logging
- scala.util.parsing and subpackages (includes parser combinators and JSON)
- scala.util.regexp
- scala.xml
(This of course doesn't include things which were demoted from scala to other namespaces like scala.util, scala.runtime, scala.annotations ...)
The list is certainly incomplete anyway...