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I think Ruby is the major banner-carrier for this feature. It is actually more awkward in Ruby to have non-trailing closures.

Scala is full of many libraries that take advantage of trailing closures. I think their standard library Future/Promise API is good example: http://docs.scala-lang.org/overviews/core/futures.html

Edit: Another popular one is the ScalaTest unit testing framework: http://www.scalatest.org

Take a look at one of the tutorials on writing a Ruby DSL. E.g. http://rubylearning.com/blog/2010/11/30/how-do-i-build-dsls-...