foreach

This should be used when you have a collection.
If you are iterating through anything that is not a collection (for example an Array) it is more efficient to use a for loop.

Single Statement

When you only have a single statement the curly bracket is optional.

Example - System.Collections.ArrayList

ArrayList myArrayList = new System.Collections.ArrayList(); 
myArrayList.Add("one"); 
myArrayList.Add("two"); 

foreach (string element in myArrayList) 
{ 

} 

Example - System.Collections.Generic.List<int>

List<int> myNumbers = new System.Collections.Generic.List<int> { 1, 2, 3, 4, 5 }; 

foreach (int number in myNumbers) 
{ 
    Console.WriteLine(number); 
}