ForEachAsync Example

/*
  To address trouble with...
      myList.ForEach( async x => ...do async work... )
  where control returns before async operations are complete,
  consider...
*/

namespace Example
{
  public static async Task ForEachAsync<T>( this IEnumerable<T> list, Func<T, Task> func )
  {
      await 
          Task.WhenAll(
              list.Select( 
                  item => 
                      Task.Run( () => func(item) )));
  }
}

/*
  The failing...
      myList.ForEach( async x => ...do async work... )
  ...becomes...
      await myList.ForEachAsync( async x => ...do async work... )
  ... and successfully awaits until all tasks are completed.
  
  BONUS! .ForEachAsync() is used fluently with the await/async keywords and is as readable as .ForEach().
*/

Your first parameter can be IEnumerable.
You may also consider making use of the Parallel.ForEach http://msdn.microsoft.com/en-us/library/system.threading.tasks.parallel.foreach(v=vs.110).aspx
It does essentially the same thing you are doing, except it will try and be smart about the number of threads it spins up at any one time.

Thanks Keboo. Updated from IList to IEnumerable parameter. Will compare against TPL Parallel.ForEach and revisit.